Now correctly sets the chosen background color and additionally sets 
another (configurable) color to the selected value.

The other  variants are basically the same as filled. The only
difference is the background color, which we are manilupating anyway.
So there is no reason to keep them.

Also for the background color directive different target elements are
needed for the different appearance variants. This is now possible.
As stylings of the old appearance are kept when changing the appearance
the styles need to be removed first.
In the moment the appearance value is changed the component is not
actually changed yet and there we need to wait for another Angular
change detection cycle, via timeout.

- Use the same font properties for input element and button element
- Change cross out behaviour. The button now behaves as
toggle button and sets the focus to the input element only when it is
crossed through.

This is meant solely as a cloze child as a representation of a radio 
button functionality.

This allows to select elements without clicking them on the canvas, as 
elements may be obstructed or not visible for some reason.

The selection logic is a bit complicated because usually only the 
overlay components are usd for selection which are also the place to 
apply any highlighting on. Here we have to find the component element 
reference from the section. Therefore the double looping 
'getElementComponent' method.

Also when an elements is selected it briefly gets z-index 100 so it is 
moved to the front and visible and manipulatable.

For all elements using radio buttons.

The value may have been null in past versions.

- Now always starts with at least an empty list.
- Compatibility handling no longer sets invalid values. This was only 
temporary anyway but it is better to not do it at all.

Now only sends a list with IDs as value. The actual list manipulation is 
done with Material helper functions (transferArrayItem...).

It is okay to discard a 0 value here, as 0 line height makes no sense 
and it is better to use the default.

Also remove duplicate CSS declaration.

Image are supposed to scale down when needed. This is done via 
max-width.
Small image shall not scale up, which is done with 
object-fit=scale-down.

Delete and duplicate buttons are no longer part of the tab view but are 
always visible below it.

The given serialized properties may not conform to all UIElement 
properties. They are merely meant as a building plan; they may also 
contain outdated properties which have to be transformed when reading.

Basically a div with border properties as usual.

Create object list, when none is existent yet. Otherwise append as 
before.

Now correctly reads the value IDs of drop list elements, so they can not 
be used again.