This required BL_ArmatureObject to have tighter control over armatures and poses. Also, (Blender) armature objects are now copied instead of shared between BL_ArmatureObjects to avoid race conditions. Also, due to the armature copy, shape key drivers need a bit of extra fiddling to get the correct armature copy. Initially OpenMP was used for threading, but then BLI_task was used due to being less compiler dependent. This commit also places time spent on skinning updates in the Animation profiler category (was previously under the Rasterizer category).