In theory, actions can now be evaluated in NLA, though in practice, we don't have an NLA Editor to create data to use this yet! Next up, transitions... Some notes: * Recoded the way the 'accumulation' methods work (i.e. blend, add, etc.), adding a few new ones. It should now be more obvious how these work. * Some assorted code cleanups done too (removing unneeded vars/args)