Rename some test-files

Remove unused property alternativeKeyboard

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