Child elements need some special CSS, for example to prevent taking up 
more space than needed.
This is only for text field and drop list, which are the relevant sub 
elements for now.

The problem that was to be solved is that buttons within a form always 
cause form validation for all form elements. Which is not wanted here.
The better solution than preventing all event is to simply declare the 
button type. As button without any type are treated as submit buttons.

A new variable is introduced for CompoundComponents: 
"allowClickThrough". With this set components can set their children and 
overlays to allow clicking on child elements or not. In the editor this 
is not wanted as the elements internal structure is different and the 
resulting event target can not be reliably styled. There we need the 
(span) overlay.
In the player though elements should be clickable as usual. The player 
can completely ignore this setting as it is on true (allowing clicking) 
by default.

- Remove fallback of TranslationService to allow empty error messages
  that can still cause red borders
- Remove the case distinction for checkboxes, since the requiredTrue
  validator also sends required as errorKey and a special fallback text
  is no longer used

They both have an element model and makes sense that a compound 
component is also a 'normal' component.

SHould now always correctly line up with the text even on different line 
heights.

Similar to a text element but parses the text on change an replaces 
markers with actual elements.
The text is then displayed inline with the elements.

This allows to use them in template bindings. Used in compound elements.

Improve general structure. Image situation still bad.

- Images now scale up and down depending on the available space.
- The new property controls the first (column) size parameter for the 
grid. The others are fixed at 1. Decimal values are allowed for 
fine-tuned control.
This prop is passed on to the child likert-row component. It uses the 
same grid and needs this info for proper alignment with the column 
headers.
- Remove unnecessary div in likert

- List items only have a margin between then but no longer on the 
outside.
- Remove unused background color. This is set dynamically in the 
template.

In ControlBarComponent the property project replaces the property
isAspectPlayer. It ensures that delays are used only in the player
and hints are always visible in the editor.

The magnifier is always visible in the editor

Required to query the elementModels of all instances of this class.

Split the code into separate methods

The MarkingService now takes care of the selection and its validation.
The text component sends its change via elementValueChanged.

This shows a outline on potential dropLists when dragging an item.

All elements now use the elementValueChanged event. Also
formValueChanged is changed.

Options and value were the same thing anyway and the value was updated 
once anything was changed within that dropList.
The player though needs a start value and this way we have one.

Supplement to commit "Refactor elements to use the model's value"

AudioComponent and VideoComponent inherit from
MediaPlayerElementComponent to avoid duplicate code

This change mainly helps the editor.
The idea is to make the element components have the correct value of
their model and don't rely on the formcontrol value. The formcontrol
can be hard to manipulate, especially in compound elements. Setting
the model value is way easier.

The formcontrols are kept and should not interfere.

- Add background to dragged element via cdkDragPreview
- Add placeholder box for dropping via cdkDragPlaceholder
- Add animations for transitions when dragging and dropping