- Use `inputmode` 'none' to hide the virtual keyboard of the os
- Use DeviceService to detect if the player is running
on a mobile device

The whole DOM structure is kind of botched. This is a quick fix and 
should be reviewed.

to ensure that a section that is not displayed has no dimensions

Call emitter in template and remove unnecessary method

Sections use the mediaStatusChanged event, which is also used to map the
interdependence of media elements

The number row has alternative keys, activatable via shift.

Also add new keys for dot, comma etc.

This can be enabled for TextFields and TextAreas and shows a keyboard
at the bottom of the screen. This does NOT set the field to read-only
which is probably wanted in a situation where the system keyboard is not
to be used. For flexibility purposes it is not implicitly set and needs
to be set manually. The same goes for other input assistance settings,
which should not be used in addition to the keyboard but it is allowed.

The keyboard has an extra switch to additionally show french special
characters.

Move KeyInputModule to the modules subfolder
Create template file for AppComponent

Rename properties and events for keypads

Rename KeyboardComponent to KeypadComponent
Rename KeyboardService to KeypadService
Split LayoutComponent into LayoutPlayerComponent and
LayoutPagesComponent
Prepare the introduction of an additional keyboard

see commit #866a33c6

Replace custom pointer events with native pointer events

By default, text fields and areas only allow the input of keys from the
respective keyboard.

and in ElementFormGroupDirective

This is necessary because the sanitizer returns now an array instead of
the modified unit definition.

Reduce the number of input parameters in FloatingKeyboardComponent
Move double-used method to KeyboardService

Instead, use Textfied component with the property isClozeChild

to avoid lint errors in templates

Rearrange the order of function calls

Replace the direct method calls in media player components with events.
For this purpose, expand the inputs of the media player components that
are defined in the ElementMediaPlayerGroupComponent.

belongs to commit #f6668bdd

- Units and element are now built via the factory. This ensures only the
  wanted properties are present. All others are discarded.
- Since the sanatizer is supposed to check the unit defintion version
  it is used by player and editor and therefore put in common.
  This in turn makes it necessary to put the JSON resolver settings
  in the root-TSConfig file.
- Renamed a couple of properties to have clearer names.