Various enchantments

Added following features / fixes:
* pusher sometimes complaining about missing fields (SHA mismatch) when sending authentication for channel, fix is backward compatible, just adds all fields from authentication object received from a server
* added ability to unsubscribe from a particular channel by name through `BLYClient`
* delegate method for channel did subscription event - since it is an internal pusher even I think following encapsulation pattern it should be handled by the library itself and not through binding events
* automatic reconnection for some reason wasn't respected when ratability changes (maybe I misunderstood original intent of `automaticallyReconnect` flag)
* Added support for `ping/pong` events that solves connectivity issues on 3G with some carriers and makes library compliant with pusher protocol version 6