Make root node position keyable.
Move assertion to better reflect what we expect to see in spe files
Fix assets to add keyed/not keyed attribute
Rename validKeys to keyedattribs

Really, we're keeping track of the names of attributes that are available in the limbs that
we have selected in the keyframe editor. That should be the only thing we're passing around,
not some index to some other list of some index or whatnot... that gets confusing fast.
Make sure to add all keyable attributes from all limbs and fix drawing routine to support it.