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.

Customized margins for paragraph elements.

This is now done via listener directly on the element overlay. The 
overlay's div is made selectable with 'tabindex'. Then the key event is 
caught and delete logic started. The actual logic did not change and 
still deletes all selected elements not just the one catching the delete 
key event.

- This helps getting rid of annoying element interaction and solves some
  selection issues (for example double clicking text elements to bring
  up the editor). While creating units, the placement and properties of
  the elements are important and not interacting with the elements.
  This is what the preview/player is for.
- This may also help with detecting selection for the Delete-key logic.

Mistake while merging earlier.

The other one used some deprecated functionality. Also we have more 
control over what is happening now.

This is now only one field with string value. Unset is put by using 
'none', since mat-select inputs cannot deal properly with null values.

Saving the actual drop down value did not work with duplicate option 
values.

This now uses "closest" to check parent nodes.
This still does not work properly since some elements can not be clicked 
and the event returns the body element. This might be fixed if a way to 
make those elements clickable is found.

This makes a small (suffix) button appear which clears all the input of 
that field.

Applies to textfield and textarea.

Variable naming issue.

All elements get the 'aspect-inserted-element' class, which is checked 
before deleting the element.

When those switches are on the size values are ignored and calculated 
automatically instead.

This avoids import cycles.

This makes checking the existence of properties for the property panel
possible, since it is possible to check for null but not for undefined.

to avoid name collision.

There are still some problems. It works a lot better than before. Adding 
this as an intermediate solution.

Before the same array reference was saved for all selected elements. Now 
it correctly creates a copy of the original array before saving it as 
value.

- Fix conditions for showing inputs. As all the properties are mandatory 
and have to be available, so no contionals are need here.
- Move CSS into the component (from parent properties component)

Importantly this includes moving logic into the classes.

... and no longer an Angular service.
This is because the IDService is needed in classes, where it is not 
injected by default.

- Remove interfaces
- Add classes for all elements as well as unit, page and section
- 2 intermediate interfaces are kept. They dont constituate a viable 
object but only additional properties, like background-color. Those can 
be added as interface to all elements. Initialisation has to be done by 
the element itself though and not by some constructor higher up.