- Make position props on buttons optional
- Move UIElement creation back to Factory instead of within Section

#294

- remove ID handling from model classes. This is now done by the editor 
itself (mainly unit service).
- Rename and move IDManager to editor as IDService

Just called from the editor, before creating the Unit instance.
It goes through all IDs and checks for duplicates. If found it generates 
a new one and shows the prompt.

- Do ID checks only in the class, not in unit service (or elsewhere)
- Fix repaired value list to get new objects instead of references to 
the existing.

Aslo create new props panel component and move border stylings to 
separate fieldset (wihtin the styling tab).

#291

One as a general label above the table and one for the first column 
heading.

Since this is no proper InputElement separate properties panel inputs 
are used.

#272

Add new parameter 'itemsPerRow'. This limits the grid columns used, 
making items move to the next row if overextending.

Also simplify component structure.

This is only useful in CompoundElements. So use checks for that class 
instance.

Now always shows the values as rich text (which works because basic text 
is valid html).

Also remove some unused fields.

Initialize to null, to be able to differentiate in the props panel.

Also improve props panel layout by always showing all fields and 
disabling them if needed instead of hiding them.

Fix translation.

Also add it to the likert row dialog.

#112

Also refactor properties panel and ToggleButton class logic for striking 
values. This now relies more on CSS classes provided by Material instead 
of doing finetuned logic my ourselves. This also allows showing the 
correct preview in the editor.

#287

- Move props to separate files
- Fix typing

Also improve media element property control layout.

#204

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

#294

Casting to ButtonElement caused issues where changed values were not 
recognized by inputs.

#280

The TipTap editor needs a setting to be able to read base64 encoded 
images.

Also improve method name.

#297

#298

..instead of multiple methods doing almost the same stuff.