Group functionality: group avatars, group updates (full support), group leaves

group functionality: 
• group avatar support 
• group update support (full comptibility iOS/android)
• group leave support
I think in some of you other code you have used a macro to help with default initializers. the NSMutableArray should be initialized to an empty array, and calls should check for count ==0 instead of !=nil IMHO. but wasn't going to do a big refactor.