SL-276 - small skeleton file tweaks to 'end' and 'connected' attributes (no functional impact on viewer)

SL-344 - fixed a problem in avatar_lad with some params in wrong group, added diagnostics to make this easier to detect.

SL-276 - move alt eyes out of face root, match coords exactly. Return face root to 3 digit precision.

SL-276, SL-344 - Skeleton and slider updates including new face joints to enable nose, eye slider controls. Increased max joint count.

SL-344.xml - avatar_lad.xml updates. During loading, error out if an attachment_point references an invalid parent.

SL-276 WIP - avatar_skeleton.xml changes, moved spine joints to  spine group, fixed position mismatch between eyes and alt eyes.

SL-287 WIP - avatar_skeleton_spine_joints.xml has 4 added joints, 2 between mPelvis and mTorso, 2 between mTorso and mChest.