Refactored iOS platform to be cleaner, more modern and more flexible.

- Split Obj-C classes into their own files, benefits are two-fold:

	* Improved clarity/cleanliness.
	* Classes are now part of the GamePlay API (read on).

- Migrated to ARC.

- Adopted modern Objective-C syntax (array and dictionary access).

- Most important; GamePlay can now be integrated into regular Cocoa Touch apps:

  * Prefixed Obj-C classes with BGP (Blackberry GamePlay) in order to avoid
    symbol clashes (Apple convention used to emulate namespaces).
  * Removed assumptions that Gameplay's viewport will be the entire screen size.
  * Added BGPPlatform Obj-C class which allows Cocoa Touch apps to set the
    active BGPViewController and provide a CMMotionManager instance.

*__Note:__ This pull request is made up of several commits, they're all related so I'm happy to squash them down into the first commit before it's merged. However, for the purpose of evaluating the pull request, the history is handy to have.*