Blender Git Loki

Added operator to remove all useless unused actions from the current
.blend file.
* From operator search, find "Clear Useless Actions"
* "Action library" actions are preserved by this operator. It targets
actions without any F-Curves
* By default, only actions which are single-user (where that user is a
Fake user) will be targeted. This can be changed to have it target any
"dangling" action that doesn't have any F-Curves
* A save/reload cycle is still required to fully remove such Actions
from the current file. Though at least now it's a simpler process to
have these semi-automatically removed ;)