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.

- Replace Material Droplist with native HTML events
- Remove simple-drop-list element; Cloze elements now use the normal 
DropList element
- Add example units

- Rewrite interface 'VopMetaData'
- Add parameter 'metadata' to VopReadyNotification

- Replace type 'any' with 'unknown'

- This corresponds to the representation in the keypad
- Prepares further adjustments to the keypad

- Name the control keys of the keyboard like those of the keypad

- Use the VeroSubscriptionService as a pure communication service
- Do not contaminate the VeroSubscriptionService with holding data

- Using scrollIntoView with target 'center' was not always reliable
  especially in FF

- The workarounds for ff with setTimeout are no longer necessary in the
  new version and have been removed
- Replace ChangeDetectorRef.detectChanges with setTimeout because the
  scroll button was not always reliably displayed at startup

Level 2 is now the level with mild logging. Level 3 does not log 
anything apart from warnings and errors.

- A HotspotImage has an image and divs placed on it, which are used
as hotspots
- Inherits from FormElementComponent, which is why the hotspots are kept
  as a list in the value property.
- Can be validated as required and uses its own custom validator

 - Remove duplicate code in keypad templates
 - Extend the use of the configuration file

- delete french keypad

- remove ID handling from model classes. This is now done by the editor 
itself (mainly unit service).
- Rename and move IDManager to editor as IDService

Use map and flat instead of reduce to set dragNDropValueObjects

- Use Unit's getAllElements method of Unit instead of
UnitUtils.findUIElements to get all DragNDropValueObjects
in UnitComponent
-Remove unnecessary timeout in UnitComponent