Add keyframe struct
Add keyframe class
Add camera class in its own file
Add keyframe helper methods to Layer.cpp

I think we should move all the keyframe stuff to layer to avoid casting
Add scrubNextKeyframe and scrubPreviousKeyframe methods
Fix interesting bug in scribblearea when pressing keys?

couldn't really reproduce consistently
Add previous and nextkeyframe actions to the menu
Merge pull request #110 from wesen/feature/navigate-drawings

Navigate to previous and next keyframes with < and >