Highlighted (background colored) text is done with mark elements which
don't have a color and make the contained text lose the styling of the
parent span, which has the text-color property.
To solve it we simply inherit the color of the parent span.

Hint and autostart functionality of videos and audios is initialized
only after dependencies to other audios and videos have been resolved.
This prevents the hint of an audio and video from starting, although
the audio is not yet enabled.

The control bar is shown only when at least one control is selected
in the editor.

The issue here is the alignment if dropLists and text fields. They are 
supposed to be exactly in line with the text which is very complicated 
with Material components, which are heavily nested and contain several 
sub-elements which need to be changed - removing margins, paddings and 
other position related styles.

Min-height should be optional for dynamically positioned elements, as 
you usually don't need it and it causes more problems than it solves. 
Elements with min-height have cause unexpected margins between elements.

- Don't use height 100%. The image is not centered but positioned
in the upper left corner

As requested by product owner.

Now scales, taking up all available space.

No unused space around images and image an text below each each other.

This reverts commit b5d3b810.

The old behaviour with non-scaling images is wanted here. Will improve in subsequent commit.

Extend the parsing to inludes h-Elements.

The explicit check for undefined ensures that the value 0 of a
number property is taken from serialized elements.

Setting on type button avoids that click events are evaluated from
the surrounding form

Before the parent elements (span, div...) were catching the drop event 
which is not intended.

The player is supposed to take all the elements already defined and 
generated in the editor. Therefore the call to generate all elements 
from the text is not a general thing but specialized for the editor.

Right now the editor does no longer generate the cloze parts on load but 
only when the text prop has been touched.

Also all elements now take the parentForm as input. Allowing it to use 
them with template binding and not only setting the value directly (in 
the controller).

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.

Button is no InputElement which causes trouble in some places. Since it 
does not make much sense in the Cloze context it is just removed.

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.

This new class makes sense logically, does not have an effect on the 
children though.

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.