Blender Git Loki

GPencil: Don't draw onion skins during animation playback

* When playing back animations, onion skinning is temporarily disabled now
so that the poses can be seen more clearly.

- I've supposedly used the check which disables this for animation scrubbing,
(I've tried both and checked the logic for each), but they don't seem to be
working as advertised. So, for now, onionskins are still visible during scrubbing.

* Onion skinning is also disabled for rendering playblasts and for file previews/
sequencer renders.