- Add "isOlderThan" method to the "SanitizationService" to distinguish
old ToggleButtons with the property "option" from new ones
- Use SanitizationService.isUnitDefinitionOutdated in Player to set
the unitDefinitionVersion (should be modified!)

Fix import order

This button helps the user to detect if a page has additional,
hidden content

DragAndDropValueObjects are now a sub-interface of TextImageLabel, which 
requires a set imgSrc and imgPosition property. (The reason is that the 
editor needs a way of generating Labels therefore needs the imgSrc set 
to something else but undefined.)

- Refactor subscriptions for verona commands

- Use done event of keyboard animation to set the scroll position
of the element
- In small browser views elements are scrolled to the top of the view
instead of the middle of the view

- problem with nullish values

- no event for elements
- only one event für presented pages

- Fix related tests

- FloatingMarkingBarComponent no longer has the elementModel property

- Error was raised when loading a second unit. It was caused by the
binding of the UnitStateService to the UnitMenuComponent

- rename variables, methods and properties
- reduce attributes for methods
- split code in sun methods

- remove prefix 'on'
- split methods