Blender Git Loki

Graph Editor: FCurve Show Extrapolation Toggle

Adds toggle to graph editor (View->Show Extrapolation). When disabled,
then fcurves only draw over the keyframe range. For baked fcurves and
ghost fcurves, the range is all sampled points.

It is intended for frequent use so anybody could assign hotkey or add
to quick favorites that's why GE-View is the best place for it.

Show Extrapolation is the default.

Reviewed By: sybren, Stan1, looch

Differential Revision: https://developer.blender.org/D10442