Destroy iOS Publisher And Android Fixes

This pull request implements the `publisher.destroy()` method for iOS. I didn't implement it for android, since `session.disconnect()` was cleaning up the views nicely on android (but not on iOS, hence the pull request).

Also, I set `sessionConnected` to false on the onDisconnected event handler. This fixes an issue that causes the publisher to get repainted (via updateView) after a disconnect.