* Move PushType to Platform Folder
- Move the PushType next to the rest of push notification code
- Specifically exclude it from needing Platform code review
- Add tests establishing rules Platform has for usage of this enum, making it safe to have no owner
* Move NotificationHub code into Platform/Push directory
* Update NotificationHub namespace imports
* Add attribute for storing push type metadata
* Rename Push Engines to have PushEngine suffix
* Move Push Registration items to their own directory
* Push code move
* Add expected usage comment
* Add Push feature registration method
- Make method able to be called multipes times with no ill effects
* Add Push Registration service entrypoint and tests
* Use new service entrypoints
* Test changes
