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 importantly, apps can now integrate Gameplay into regular Cocoa Touch apps:

  * Renamed overly generic class names that are likely to clash
      e.g. AppDelegate -> GameplayAppDelegate
  * Removed assumptions that Gameplay's viewport will be the entire screen size.
  * Added PlatformManager Obj-C class which allows Cocoa Touch apps to set the
    active GameplayViewController and provide a CMMotionManager instance.