Updated wizCanvasView to handle application lifecycle notifications.

- This adds support for pausing and resuming the canvas rendering and fixes
  crashes games were experiencing when moving into the background.

- This adds support for reducing the amount of memory used by the canvase in the
  event a memory warning is received.
Merge pull request #16 from wcwynn/v1.9-lifecycle-notifications

Updated wizCanvasView to handle application lifecycle notifications.