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

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.

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.

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.

Since this is built using a grid it does not need dimensions. In fact it 
having dimensions interferes with styling.

For elements which don't have this functionality the workaround is to 
use pointer events and make the elements unclickable.

* Add IntersectionService
* Add CompoundElementComponent as parent for LikertComponent
* Inject ElementRef to common ElementComponent
* Rename players' ElementComponent to ElementContainerComponent

Other elements do implement the interface but do nothing with the 
property. This make all the interface handling a lot easier at the cost 
of having useless variables in some contexts.

* Remove FormService Injection
* Move FormService and form types to player
* Move interface ValueChangeElement to uI-element.ts
* Use interface InputElementValue instead of
string | number | boolean | null

* Add `InputElementValue` as type when needed

Colors and font stuff.