Loupe doesn't always dismiss

[RSully]

To reproduce on the view controller branch:

• Press and hold on the color picker view
• With another finger tap a button to push another view controller to the stack
• Let go of where the loupe was being held down
• Tap the back button and notice the loupe is still open

[RSully]

By checking the value of self.window within didMoveToWindow we can remove the loupe when no window is present.

This branch also includes some performance enhancements within didMoveToWindow that prevent us from rerunning genBitmap if the old size is the same as the new size.

This branch also includes the commits I had tested separately to move the demo into a UIViewController subclass and include a button to push more to the nav stack for testing performance.