Several elements were broken after updating the Material library.

Add new component for combobuttons, which allow selecting and applying a 
value in one connected element.

#294

Now the dialog scrolls and the buttons at the bottom can be reached even 
on low viewport height.

#294

The material dialog functionality used, adding the mat-dialog-title 
directive the toolbar.

Set back to the default setting to prevent CSS settings to spill over 
into other parts of the application.

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.

This may destroy alignment of inputs and produce unwanted scrollbars.

Input elements are now grouped in fieldsets.
They also a cool gradient background color.

Highlighted (background colored) text is done with mark elements which
don't have a color and make the contained text lose the styling of the
parent span, which has the text-color property.
To solve it we simply inherit the color of the parent span.

- Reordered the buttons to make it look nicer (but still make sence 
logically)
- Put some more divs with flex layouting to prevent elements moving 
unexpextedly.
- Changed color and list inputs to split-buttons. Those compone a button 
with a dropdown.
- The editor now saves the set color and  it can be applied to 
subsequent selections as well.

And avoid global styling.

This improves bold text readability.
This has to be done in the actual element, in the TextEditor and on the 
properties panel.

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.

Based on TipTap which in turn is based on ProseMirror. No further assets 
are needed.