Blender Git Loki

Improved hotkeys for frame/keyframe/jumping

Thanks pepeland and 3duan for the suggestions. I've been looking at
improving these for a while...

* Left/Right Arrow = Single Frame stepping as before
* Up/Down Arrow = Jumps to next/previous keyframe (used to be the
uncomfortable Shift PageUp/Down)
* Shift Up/Down Arrow = Jumps forward/back in 10 frame increments
(used to be Up/Down Arrows). 10 frame increment should get
customisable again as in 2.4, but need to find some UI space to put
that!
* Ctrl Shift Up/Down/Left/Right = Jump to start/end frame (used to be
Shift <Arrow Key>)