The native browser-drag-and-drop does not work in tablets. Therefore 
back to Material which works.
Features are moved over with the exception of replacing items.

- Copy-Lists now always allow putting items back.

- Renew example files
- Update versions and notes

- Add cdk scrolling strategy to keyboard that brings overlays to
scrolling

- Set the duration of highlighting anchors to 15 seconds
- Disable simultaneous highlighting of anchors

This reverts commit f90bcc5b
Target installation seems not to support this Verona Api version yet

Uses external software 'MathLive'.

Distpacker issues with mathlive have been solved in a custom 
distpacker.ts in scripts-folder. This is now used instead of the 
distpacker from the npm package.

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