#25 Rethink Scope handling

[Lars Heuer]

Rethink IScope handling for variants.
Problem: A SET_SCOPE event is sent, but the variant does not contain the name's scope, it is computed dynamically. This is bad for the ScopedIndex since it needs the complete IScope for updating.

Current solution works but is far from being ideal.

Options:
- Reintroduce the ADD_THEME / REMOVE_THEME events
- Handle the scope for variants differently in the ScopedIndex (ScopedIndex has to be refactored anyway)