- Reformat styles

Components with bigger scope are put to the component root, canvas, 
props panle and new-element-panel.

Remove unused class.

The solution is to always show the section menu of the selected section. 
No more hovering shenanigans.

#223

This is now done only via the cdkDropListGroup directive which collects 
child drop lists. There is actually no need to connect them manually.

Now uses the implicit grid in auto mode.

This is done according to the Angular best practices and minimizes
namespace collisions when using other packages which might use the same
selectors.

Technically the selectors are not even becessary since we use an Angular
component factory to create element components but it is still useful
for the DOM element naming, for debugging purposes for example.

The dropListList generation is now done when things are changed via the 
section menu and no longer on element update via unit service.
Also remove some interfaces to avoid circular imports. The interfaces 
are so small and insignificant that their form might as well be 
specified at usage point.

This allows to select elements without clicking them on the canvas, as 
elements may be obstructed or not visible for some reason.

The selection logic is a bit complicated because usually only the 
overlay components are usd for selection which are also the place to 
apply any highlighting on. Here we have to find the component element 
reference from the section. Therefore the double looping 
'getElementComponent' method.

Also when an elements is selected it briefly gets z-index 100 so it is 
moved to the front and visible and manipulatable.

This reverts commit c71cf1a2.

Need to bubble the event further up to where there is a section 
reference.

This structure moves closer to the structure template the team decided
on. Components and services are kept in dedicated folders instead of
following the logical code structure. This is still not the case here as
the unit-view component is still nested, but it's closer.

Was missing margin at the top.

By clicking anywhere but elements of the side panels.

The main components are right at top level and the directories below
mimic the data structure (unit->page->section).
The toolbar is only used in dev mode and does not belong directly to the
unit view.
The TextEditor is a complex component and deserves it's own directory
even though it is used within the unit-view. Might be refactored to its
own module later.

The duplication is done by creating a new element (UnitUIElement)
for each element of the copied object. And then overwriting it with
the props of the old one, in addition to assigning a new ID.

Can now be repositioned and moved between sections properly.

- The selection service only needs to handle element selection. For
pages and sections having the index is enough.
- Those indeces are simple fields instead of observables. This also
simplifies the components which don't have to get the value out of the
observables.
- Therefore the selection service does no longer need to have a direct
reference to the unit service and it's unit.
- Selection logic is not done by the section components themselves but
by the parent canvas component.
- The unit service can now manipulate pages and section by index in
addition to passing the necessary objects directly.

When maxWidth is not set it now correctly ignores the prop is takes the 
default 900px.

And having the correct grid coordinates.
Also refactored the canvas sections to be different components.

The section menu (containing all former properties options and
reordering) is now shown on section hover.
- With the removal of the section edit mode the view-only elements
are no longer needed, as sections can no longer be dragged.
- The unit service now has a unified logic for moving items in an array,
being used for pages and sections. Although for pages there is an
additional regarding the always shown page.
The reorder function silently ignores nonsense reorders!
- The prompt dialog now takes the text as parameter

They are now modified via menu at the section and no longer via props 
panel.

To make it work that the section itself can handle drop events, but
also have the canvas to handle drops when outside of the section, all
the allowed dropLists have to be connected. Because the lists are not
properly nested (see below), this needs to be done manually by IDs.
This list is given to the necessary dropLists to make it possible to
drop items not only into them but also any other connected dropLists.

Dynamic sections have droplists for the grid cells next to the actual
elements. Elements can not be children of the grid cells because they
can span over multiple cells.

Dynamic sections don't have a general drop area, like static sections.
They have grid placeholder elements which are droplists. Therefore they
have no parent dropList to add to the list but themselves.
Static elements only have the parent, which is added to the list.

Resizing in dynamic sections is handled by the section/element-overlays
themselves.

Ticket #38

The button is hidden when there is only one section. There always has to 
be at least one section.

Ticket: #35

When this is set the page will only be rendered to that width. Otherwise 
100% of the available space is used.

Use global style for droplist cursor.

In this mode sections can be inserted, reordered and deleted with 
buttons directly on the canvas.

Also refactor unit service to use more it's own selection variable 
instead of using passed references for manipulating objects.

- ... mostly for dynamic positioning
- Refactor reordering of sections. They can now be moved by small
buttons to the side, which appear when hovering. The section edit mode
is no longer available. -> KISS
- Removed all toolbars. The props can now be set via the props panel,
which now has sections for pages, sections and elements. This is to have
more vertical space available for editing the unit.
- Sections can now (only) be added via the toolbox panel, where the
second tab is now exclusively for sections. Future templates are
supposed to be whole sections, which can also be added from there.
- Refactor CSS layouting (flex and co) to have better handling of
vertically growing page (via sections)
- Some preparation for an upcoming overhaul of selection stuff
(again :))

- UnitService no longer knows about selection. Now needs element to be
manipulated, as param.
- Add new SelectionService handling selection of canvas elements. No
sections yet.
Move eventing stuff accordingly.
- Canvas Section now creates it's child overlay component in the
template instead of dynamic component creation. This make event handling
easier und is more the Angular Way. Also removes a lot of eventing and
selection handling from the component.
- Aligment of selected canvas elements in done in UnitService. That is
where all unit manipulation should happen.
- More takeUntil