Blender Git Loki

Pose Library: remove assumption about Action group names

Remove the assumption of the pose library that Action groups are named
after the bones in the armature. Even though this assumption is correct
when the keys are created by Blender, action groups can be renamed. Keys
created by Python scripts can also use arbitrary group names.

Since there is more code in Blender making this assumption, and looping
over selected bones is also a common occurrence, this commit contains
some generic functionality to aid in this:

- `BKE_armature_find_selected_bones`: function that iterates over all
bones in an armature and calls a callback for each selected one. It
returns a struct with info about the selection states (all or no bones
selected).
- `BKE_armature_find_selected_bone_names(armature)` uses the above
function to return a set of selected bone names.
- `BKE_pose_find_fcurves_with_bones()` calls a callback for each FCurve
in an Action that targets a bone, also passing it the bone name.