Hierarchy-interaction test, Fix fro Andrej

Added a new feature to the InteractiveRenderer:
- When holding shift while picking the shape is temporary replaced by
its parent. The highighting-logic works fine, but it looks like there
are some positioning problems.
- Added a helper function for resolving a shape from a picked mesh.
- Added the keydown and keyup handlers.

Since Andrej did not fix the issue with his initial code, I have
finished it for him so that everybody can fork.