- to prepare markable support for text as compound children

#656

- Toggling of keyboard and keypad are now async
- Keyboard and keypad animations are disabled for a short period of time

- Input field manipulation moves from service methods to new
  TextInputGroupDirective

#461

- Use own StateVariableStateService which uses the same new base class
as UnitStateService

- Only elements with this property are considered in the player when
determining the presentation state
- Add the registration of CompoundElements at the UnitStateservice
- Fix visibility handling of section with simple rules

- Basic implementation

Also restructure files containing interfaces.

Displaying a message is task of the host
#398

This was necessary because the new text selection action of the button
is not a navigation.

- Areas are marked with the surrounding 'aspect-anchor' tag

- If this property is set, the input of more characters than specified
in maxLength is prevented
- It also prevents the insertion of text.

Fix import order

- remove prefix 'on'
- split methods

This way elements can handle their logic themselves without having to
rely on outside utility classes.

Also restructure files in common in a more logical way.

Knowledge of the 'document' existence is only a matter of the function 
not the caller.