This structure moves closer to the structure template the team decided
on. Components and services are kept in dedicated folders instead of
following the logical code structure. This is still not the case here as
the unit-view component is still nested, but it's closer.

Now correctly uses the multiline dialog.

Use global styles and remove unecessary styling commands. The dialog 
window will mostly size itself.

Use separate method with a name to know what this nested loop is for.

Before the children were simple javascript objects missing the methods 
of out proper typescript objects. Not it correctly calls the constructor 
on all row elements instead of just assigning the value.

Read the formerly used 'options' array.

All elements now use the elementValueChanged event. Also
formValueChanged is changed.

Also reorder translations a bit.

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

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.)