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

Since the options of the DropListComponent are now managed as values,
the DropListComponent can be treated as a standard FormElementComponent

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.

Does no longer change the options instead of the connectedTo array. I 
reworked some logic that before only changed the options to now be able 
to handle any kind of string list.

Improve detection of valid pages, sections and elements

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.

In the UI. Internally it is still likert.

The player-element dialog options did not show the field, even when it 
has a value. Now it properly checks of the existing config has this set.

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 includes a fix in the dispacker, which no more tries (and fails) to 
replace variable names.

It logically belongs there since it is no compound element and also 
needs to be near the other radio group.

Now correctly shows a dropdown instead of a text area.

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

When selecting the preset value, sometimes the string is empty and it is 
not possible to differentiate the options. Therefore an index is added 
making it possible to reliably select a value.

Use the status of each element