Blender Git Loki

GPencil Onion Skinning: Setting before/after to -1 will turn off onionskinning in that direction

This is an experimental option that I found would have been useful to have,
when making my earlier anim test. The only contentious point is whether it's
better to use a separate boolean flag (perhaps bound to the labels) instead
of overloading this setting (and describing the usage in the tooltip).