- 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

- TextAreaElement
- TextFieldElement
- TextFiledSimple
- SpellCorrectElement

- 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

- Add the new features from version 3.7.0
- Fix the entries from version 3.8.0

- Using the Geogebra method 'getBase64' is very resource intensive.

- 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

This is necessary to avoid playing parts of audios and videos twice
when a unit is reloaded, since audios and videos send their playback
time only every 5 seconds when they are played back.

- Make sure that the textarea has been displayed once (AfterViewInit)
  before its dimensions change again

- The width of the border is no longer needed because
"box-sizing: border" is used
- Scaling of the inner triangle areas is replaced by the setting of 500%
 width and height to be able to fill the whole area of the obtuse
 triangles and at the same time not change the width of their borders

- Also simplify the button constructor

- add hotspot image element
- raise version to 3.8.0

Rework LogLevels and adjust log statements

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