WIP refactor of SceneViewController into a cluster

Refactor of SceneViewControllerFor… classes to be parented by a single SceneViewController base class.

• New SceneViewController base class, which absorbed the common functionality from the SceneViewControllerForCG/GLK classes.
	» measuredFramesPerSecond, storeRecentUpdateInterval: and storeRecentDrawInterval: functionality and the _recentUpdate/DrawIntervals RecentIntervalSamples storage centralized from SceneViewControllerForCG/GLK
	» Scene property also centralized from SceneViewControllerForCG/GLK
	» cluster class, preventing its own initialization and replacing itself with and instance of the right child class.
	» Finally figured out and cleaned up the init path; per the iOS docs' “Multiple Initializers and the Designated Initializer”, now initWithScene: is the designated initializer calling super's initWithNibName:bundle:, and initWithNibName:bundle: is overridden to call our own initWithScene:.
	• `UIViewController <SceneViewControllerProtocol>` changed to `SceneViewController` all over the place.
• SceneViewControllerProtocol renamed to ContinuallyDrawingViewControllerProtocol, and moved its Scene-centric init and property to SceneViewController.

Also:
• SceneViewControllerRecentIntervalInfo/SceneViewControllerUtil renamed to RecentIntervalSamples, and its measure… and store… class methods became extern functions, and changed a bit.
• AppDelegate now mostly deals with SceneViewControllers directly, rather than adherence to SceneViewControllerProtocol.
• Project file updated accordingly

Danger: Currently does not build.
Renamed to AppRootViewController

Renamed RootViewController to AppRootViewController.  It just seems to make more sense, following the name of AppDelegate.

I think I'll start using “App” as a prefix for anything non-reusably app-specific, like it's a special Obj-C namespace (so one would never see “SDTApp…” just “SDT…”, “App…”, or otherwise).
Compiling, Working SceneViewController cluster

Big stuff:
• SceneViewController now has isCluterBaseClass and isClusterSubClass methods, used here and there.
• SceneViewController implements all of ContinuallyDrawingViewControllerProtocol's properties with stubbed implementations that'll raise not-implemented exceptions unless overridden.
• Scene gained a renderMethodDescription method (two different meanings for “method”), implemented in subclasses SceneForCG/GLK.
• OverlayVisRep now uses Scene#renderMethodDescription to display the named of the render method, and checks the current whether it should try to show the FPS by comparing Scene-to-Scene, eliminating the dumb _usingGL ivar.

Little stuff:
• Further switch-over from `UIViewController <ContinuallyDrawingViewControllerProtocol>` to `SceneViewController` in AppDelegate.
• Added missing GLKit.h import to SceneViewControllerForGLK.
• Removed old SceneViewControllerUtil junk.
• Changed RecentIntervalSamplesMake() from using inline to NS_INLINE (which is a compiler-differentiating `static inline`).
• RecentInervalSamples.m's calculateFPSFromIntervals needed a forward declaration.
• RecentInervalSamples.m added to the project file.
Fixed measured FPS coming out as “NaN”

The main issue was that the wrong (subclass only) SceneViewController/SceneViewControllerFor…#setupInternalState method was getting called; eliminated the method in favor of just doing the initialization inside the appropriate init… method.

Also improved the rendering of the FPS text to check for invalid values (infinity, NaN, zero or near-zero) and display “---” instead of the number.
Switched over to using SceneViewController's init

Switched AppDelegate over to using the SceneViewController cluster base class's initWithScene:, and only differentiating its SceneViewControllers by name, not type.  Discovered that I had a bit more work to do in SceneViewController's init…

• Created a NSMutableSet of sub-classes of SceneViewController, created a registerClusterSubClass: class method, and put in calls to it in the SceneViewControllerForCG/GLK::load methods (all similar to the opening recommendation in http://www.cocoawithlove.com/2010/01/getting-subclasses-of-objective-c-class.html)
• Created a meant-to-be-overriden canUseSceneClass: method, and implemented it in SceneViewControllerForCG/GLK to judge the Scene's Class.
• Implemented an internal subClassForScene: method that checks registered sub-classes until it finds one that works, and used it in initWithScene's cluster-class init dispatch.
Merge in branch 'refactor/SceneViewController-base-class'