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

Merge the `unitDefinition` with the `unitState.dataParts` to insert the
saved values

Required to decide whether the `section` or `element` should be inserted
or appended to its `formArray`

Required after changes in element components
(commit: 9e3c0613)

- ... 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 :))

Sections and elements can have this prop. Elements only need it to 
determine what properties to show in the props panel.
The others are basic props for grid layouting. Refer to the grid 
documentation.

This is in preparation for dynamic layouting.
The actual dimensions are set by the overlay component which differs but 
is existent for both editor and player.

* Remove workaround with `Promise.resolve().then(() => ...`
* Use `changeDetectorRef.detectChanges()` after updating the validators

Make the initialization consistent

Getter work like functions and are executed every time Angular change
detection runs.

* Since always visible pages are removed from the order, form
arrays must be rearranged
* Refactor getter as properties in `PlayerStateComponent`. Getter
work like functions and are executed every time Angular change
detection runs.

* Create `FormGroups` without ids
* Add `FormArray` for elements

* Add section array to the form groups of the pages
* Remove unnecessary component factory from `SectionComponent`

Replace pageIndication with translate pipe

* Add specific translation file for editor in assets/i18n
* Add first translations for toolbar

Refactor some translations

more information about [ngx-translate](https://github.com/ngx-translate/core)

In addition to the scrollable pages, units can also have one page that
is always visible.

- 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

Use `massageService` of common project.