Renaming some methods to more closely match the standard in Objective-C.
Fixed prefixes to change from NS and UI to BTV (BubbleTableView).
Added method for scrolling to the bottom of the chat window on activity and as needed.
Updates for ARC and to fix some compilation warnings.
Finished the renaming (some UI* and NS* were still present)
Fix ARC build

I'm not worrying about putting in the #ifdefs to make this compile under
non-ARC. Code that conditionally compiles for both modes is silly; just
set the ARC compiler flags appropriately for each source file.
Allow messages to not have bubbles or avatars

New properties .hasBubble and .hasAvatar on BTVBubbleData.
They default to true but can be set to false.
This is useful for announcement-type messages.