Remove unused class.

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

- Add fieldset to make it look nicer.
- Improve image to have fixed size, scale properly and show buttons only 
on hover.
- Improve translations
- Add tooltip to actionparam dropdown: When having selected pageNav it 
shows a tooltip to get across that only valid pages can show up.

#240

#243

For now only consisting of unit tests.