* Fixed some retain cycles that were preventing the RMMapView from deallocating

There seem to be quite a few memory leaks caused by retain cycles. 

https://github.com/Alpstein/route-me/issues/102
https://github.com/mapbox/mapbox-ios-sdk/issues/221

I have fixed a few of these with this commit. You can reproduce the leak easily by pushing a view controller with a RMMapView onto a Navigation Controller and popping it off again.