cleanup of Avatar:: and MyAvatar::render()

MyAvatar now calls Avatar::render() which does most of the work.
Also, made ::renderBody() a proper virtual function
Merge upstream/master into "no-hands" project
cleanup: AvatarData doesn't derive from NodeData

Cleaner Interface since the AvatarData is already not the NodeList.
Reduces overhead/confusing code when parsing packets from AvatarMixer.
Merge upstream/master into "no hands" project.
fix bug: bad offset into avatar data during decode
remove dupe hand data from avatar updates

partial progress toward issue #2256
change wording of comment
don't send redundant head rot and hand pos info
Merge upstream/master into cleanup project
bump version of PacketTypeAvatarData from 1 to 2
Merge pull request #2338 from AndrewMeadows/cleanup

Don't send redundant avatar hand/head data, and cleanup.