Fix inset of messageBubbleTopLabel when there is no avatar
disable send button when setting custom send button. fix #479
Merge pull request #495 from piercifani/fix-bubblelabel-allignment

Fix inset of messageBubbleTopLabel when there is no avatar
tweak #495
fix rendering and size calculations for custom fonts. close #490. close #489. close #407. close #347. credit @ghazel
fix unit tests
fix #498
bump version nums
Merge branch 'develop' into release-6.0
refactor library for core media message support. refactor JSQMessage to be abstract base class. add JSQTextMessage. add JSQMediaMessage. add JSQMessageMediaData protocol. Update demo. ref #223, #476.
remove demo class prefixes
update project assets
finish updating demo assets. #502
unit tests
optimize avatar loading. check layout avatar size first, if zero don't even ask delegate. change default avatar size to 30.0.
update xibs for xcode6, iOS 8. refine and streamline JSQMessagesCollectionViewCell.
add demo photo asset
update collection view, controller, and cells for custom media reuse identifier for media message cells. #223
add concrete JSQPhotoMediaItem for photo messages. ref #223. update demo handle media messages
add functionality to didPressAccessoryButton: in demo