- Replace top layer with inline editor
- Make keypad and keyboard available for TextAreaMath

This was changed without reason, but is actually a good (default) value.

1. Check if an alias is present, so that the constructor creates one.
2. Only register the value IDs, when creating a valid element. Invalid 
elements generate and register IDs in the constructor (else path).

Disallow state variables without alias.

They are registered when being created.

#713

This method is the same for all elements and can be implemented in the 
parent.

#703

This may happen when changing the Clote document property.

Also move cloze-code into Cloze and no longer have it in a general 
purpose service.

The default value of the child class overrides the value set by the 
parent constructor.

#700

#700

#702

#706

#702

#704

This service is unused for a long time.

Now the paragraphs are shown actually below each other and not next to.

#699