Blender Git Loki

GPencil Stroke EditMode: Replace 3D view menus when in stroke editmode

After playing around with the current workflow the other day, it became clear
that the current editing workflow could still do with some tweaks to be more
convenient.

* To make it less confusing/ambiguous what "mode" we're in when editing
Grease Pencil strokes, and also to provide another way of seeing all
the available operators, the Select and "Edit" menus in the 3D View
header now show Grease Pencil specific lists of operators now.

* Also, added a quick-access button to the header to toggle onion skinning.
Even with the Pie Menu and the Properties Panel, the existing ways of
quickly toggling this aren't good enough.


TODO:
* The "Mode Selector" is now the next target to tweak. As Strokes EditMode is not
a per-object setting, but rather, per GPencil datablock, this will be quite hairy
to hack around.