link to detailed instructions for custom cells (#1828)
link to detailed instructions for custom cells (#1828)

Many people were having problems subclassing from `JSQMessagesCollectionViewCellIncoming` and `JSQMessagesCollectionViewCellOutgoing`
TeletronicsDotAe/JSQMessagesViewController,adozenlines/JSQMessagesViewController,adozenlines/JSQMessagesViewController,adozenlines/JSQMessagesViewController,sebastianludwig/JSQMessagesViewController,sebastianludwig/JSQMessagesViewController,Lucashuang0802/JSQMessagesViewController,jessesquires/JSQMessagesViewController,Lucashuang0802/JSQMessagesViewController,TeletronicsDotAe/JSQMessagesViewController,derekjcarter/JSQMessagesViewController,Lucashuang0802/JSQMessagesViewController,TeletronicsDotAe/JSQMessagesViewController,sebastianludwig/JSQMessagesViewController,derekjcarter/JSQMessagesViewController,jessesquires/JSQMessagesViewController,derekjcarter/JSQMessagesViewController