Prevent double emitting of event when value and status are changed

Use "display:none" instead of "*ngIf" to hide the section and make sure
its children are loaded.

- remove TODO

Exceptions
- BACKSPACE, RETURN, SPACE (like iPad)

- Remove TODOS

elementModels are described in the unitDefinition
elementCodes are saved in the unitState

Their values are mapped by the ElementModelElementCodeMappingService

for type text and image

- Rename class name, methods and properties
- Remove method registerDropListValueIds
- Calculate array of DragNDropValueObjects in app component

Use the mapper method `toUnitState` of the UnitStateElementMapperService
when registering elements and their initial values

Use configuration and refactor keyboard template

The sanitizer is now a service, so it is testable.
Since it uses the IDService it needs to be a real service as well.

Both are used by the player therefore moved to common.

Delete keyboard module

This is possible since now playerState also has the information of the
underlying scrollPages

since the player uses it as well

- add unit-definition-menu module
- add verona module and move verona services and verona interfaces to it
  to make them available in different modules
- move the distinction of different page types to app component to make
  them available for unitDefinitionMenu component

Overwriting styles of HTML elements can lead to unwanted side effects