Push Project: abstract device storage:
 - introduced interface IDeviceManager
 - added InMemoryDeviceManager
 - added FileDeviceManager
 - PushManager accept IDeviceManager to add/remove devices
 - if DeviceManager implements IDeviceStorage, additional save/load logic involved
Push Project: GCM: wrapping cloud json response with nice class structure + handling errors
Merge pull request #1 from remobjects/develop-crossplatform-sandbox

improovements to GCM part