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.

Interactions are mutually exclusive (for now). The string values 
describe which interaction is possible.

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

Although the DropListElement is a FormElement, its value is represented
by the field options. Therefore, this state must be saved.

The drop listener simply does nothing when this is set. This way it is 
still possbiel to drag item but dropping them has no effect.

It needs row and column to work. (It is using flex in the background.)

Use 'horizontal' and 'vertical'. Which are better terms and also align 
with other element's values.

Also improve conditional border style. The additional dragPreview is 
needed so the dragged item does not have the border.

The width/height of 90% are a preliminary workaround to not produce 
overflow with the border. A better solution would be good.

This element has a list of string as editable options. Those strings 
form draggable elements which may be reordered or moved between 
different DropList elements.

Also refactor option change logic to allow any property not just the 
text property.

This works similarly to the standard radio group, but has a fixed 
horizontal layout with images above the options.

* Change the detection of the parent element to determine whether the
audio/video player is running in the aspect-editor or the aspect-player

* Add magnifier properties to `ImageElement`
* Set used value at `UnitStateService`
* Bypass parsing error of distpacker

Wait until a solution is found for the distpacker when parsing "'url('+ (image.src) + ')'".

Use flex to position image and text below one another. Don't use any 
image scaling setting. Now the images grow but don't shrink.

There were some things missing when renaming questions/answers to 
rows/columns. Now everything is properly named.

* Show current and maximal runs in control bar

This function will be implemented differently.

* Refactor markable text
* Prevent multiple selections (feature is only supported in Firefox)