Blender Git Loki

Animation: Allow selection of FCurve + its keys

Selection of an FCurve with box/circle select now selects the entire
curve and all its keys:

- Box selecting a curve selects all the keyframes of the curve.
- Ctrl + box selecting of the curve deselects all the keyframes of the
curve.
- Shift + box selecting of the curve extends the keyframe selection,
adding all the keyframes of the curves that were just selected to the
selection.
- In all cases, if the selection area contains a key, nothing is
performed on the curves themselves (the action only impacts the
selected keys).

Reviewed By: sybren, #animation_rigging

Differential Revision: https://developer.blender.org/D11181