- Use own StateVariableStateService which uses the same new base class
as UnitStateService

In Player-context the constructors are to fail, when the given 
properties are not exactly as expected. Therefoore they are validated. 
When this validation fails, an environment variable is checked to 
determine if the element should be created anyway with defaults. This 
switch is off in player-context. But the Editor is not so strict and can 
create elements with incomplete parameters.

There is also a new VersionManager which checks given unit definitions 
for version-validity. Upon failing this check Player and Editor show 
error messages.
The Editor accepts a certain unit definition version, but shows a 
warning.

The Editor checks units for invalid references after loading. If any are 
found, they are removed and an info-panel is shown.

- Remove SanitazationService from player
- Extend interface ButtonEvent

#401

- Refactor directive

- Basic implementation

Also restructure files containing interfaces.

Most importantly remove the standalone switch and let the service always 
send postMessage, even when there is no surrounding application 
listening. This helps testability and has no downsides.

Also:
- Make methods static where applicable
- Remove useless variables and methods
- Improve variable initialisation (to allow undefined)

- Areas are marked with the surrounding 'aspect-anchor' tag

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

- 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

- Sanitize without using unit definition version

- 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 related tests

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

This way elements can handle their logic themselves without having to
rely on outside utility classes.

Also restructure files in common in a more logical way.

Reloading a UnitDefinition includes loading the current UnitState

This eliminates the need to specify the different page types in
AppComponent