[Bf-funboard] better onion skin support

[Oscar Dario Franco Galeano]

Hi

When I have onion skin, or view keys activated in a mesh I can see the keys
in other color through the 3d view, but this can't be compared to a real
onion skin because if I change the IPO curve I can slow in or out the
movement, the ideal would be to see the next and previous frames, and
configure it to see every 1, 2 or n frames, just like the armature ghost is
working right now

I'd like also to be able to activate the onion skin in non selected meshes,
what if I have several meshes controled by a single armature and I want to
visualize not the armature ghosts but the actual movment of the meshes? it
would be a frame driven onion skin, not a keyframe driven one, and being
able to activate it in multiple objects at the time

thanks