Fix crash when deallocating a drawer view controller that was never loaded.
Accomplished by removing key value observation only if the view is loaded. View loading is where we establish observing.
This fix is important for unit tests where the application UI may partially load: instantiating classes and relationships but not view hierarchies.
Change unsubscribe kvo crash fix to be more robust.
Simplify kvo crash fix. Subscribe to pane view in `-initialize` instead of `-viewDidLoad`.
Replace hard-coded KVO string with string from selector.
Merge pull request #61 from fcanas/master

Fix crash deallocating a drawer view controller that was never loaded.