Add Uuid object to ScriptEngine
AvatarData stores its sessionID
AvatarData now stores sessionUUID
merge upstream/master into andrew/scripting
sessionID --> sessionUUID for consistency
use slot to change AvatarData::_sessionUUID
update boiler plate to abide by new standard
fixing formatting
Merge pull request #2630 from AndrewMeadows/scripting

Expose MyAvatar.sessionUUID to JS