For dynamic section we keep the solid line as the dashed one is harder 
to see. Needs to be discussed maybe.

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

Compound elements are now supposed to use overlays for their child
elements. This overlay makes selecting child components (by clicking on
them) and marking them as selected (done by the selection service)
possible.
The SelectionService no longer needs special logic to handle compound
children selection, as they now also have an overlay with the same
interface as normal (canvas) elements.

A few modifications in connected directives are necessary. The now
handle children components in a proper array instead of QueryList.

Likert elements do not have clickable children yet and work a little
differently. This should probably be unitized in the future.

Lower and the input element panel does not show properly.

This way the dialog does not grow too wide, when lots of text is 
entered. There could be a lot more logic here to calculate exactly how 
big the window should be, but that seems like overengineering right now.

- 'hideOtherPages' is not supported by verona api
- 'uninterruptible' is already fulfilled by disabling pause and
progress bar

Refactor MathKeyboardComponent to reduce code size

Was not working at all before. Now the logic is much simpler with the 
use of tiptap attributes.

Was broken after previous refactoring.
The renderHTML method only works with a proper return. Don't know why. 
Therefore disregard the linter warning for now.

Cloze no longer has a text property and needs a way to open the 
TextEditor.

Now manages it's width and height itself.

Also has some new properties:
- verticalOrientation should be self-explanatory
- dynamicWidth allows the user to set a width manually. The buttons on 
the element automatically stretch to meet the set width (or height).

- Naming
- Focus after nodeview insert

Also editor in cloze mode now respects the element's font size.

- Now only has a variable 'document'. This holds the HTML representation
  in an object. This object is enriched with element models.
- Because the the TextEditor extension can neither create multiple
  element instances nor use the IDService to generate their IDs, this
  has to be done afterwards. See ClozeParser.
- The cloze element has rather extensive compatibility handling because
  cloze elements used to save an actual HTML representation. This has to
  be transformed to JSON/object. Therefore we replace the old backslash-
  markers with custom HTML tags. The editor object does this
  transformation. It needs some custom extensions to recognize (and
  don't remove) the HTML tags though.
- Cloze now shows a placeholder text when empty
- The cloze component needs a small pipe to extract text formatting
  options from the paragraph parts.
- For getting the child elements for the player the models have to be
  extracted from the somewhat complex (JSON)document.
- Added some rudimentary interfaces for the TextEditor document format.
- Removed the old ClozePart interface. This is quasi part of the new
  interfaces.

- Give proper name
- Fix variable names
- Fix deprecated methods

- Improve variable naming for unit definiton type. (version string)
- Use 'iqb-aspect-definition@1.0.0' as value which better communicates
  the purpose of the data.
- Also update the HTML files with the new definition. (Even though it is
  not checked anywhere.)

Before only the 'parts' parameter was saved. Now the HTML text is saved 
as well, so future versions can properly restore the element.

The copy is needed to not have cross references between elements.

This dash is a bit shorter.

This a top/99/double quote.

Also reorder the special chars a bit some it looks nicer.

The line-height setting on the before and after selectors are so the 
quote does not reserve space.

This is for the different use saces of a simple text element and a cloze 
element. The latter needs more inputs for child elements and also return 
JSON instead of HTML.

The NodeViews are for the TextEditor to render Angular components, which
now serve as preview instead of the old backslash escaped characters.

All extensions are now placed in a specialized directory. Except the
NodeView stuff which is kept together.

Was missing the actual change of the variable.

Also improve tooltips.

- Fix reading values from combinedProperties object. This object has the
needed property in its root.
- Don't show alignment buttons in dynamic mode
- Make the small input fields a little wider so the placeholder text
does not overflow, when there is no valid value to show. This may happen
when multiple elements are selected, which have differing values.

- Move the method to the unit service, so the proper 
updateElementProperty method can be used.
- Also improve the logic, reducing variables.

Only select the element component when it is not already selected. This 
prevents delesecting elements which have been multiselected.