Added BaseApplication with loading view

Now if a controller has an unresolved `promise` attribute then the
BaseApplication's `showLoadingView` will be called and will, by default,
instantiate and display a LoadingView (also new) with the controller's
`loadingMessage` attribute (or "Loading..." by default) and the
controller's `loadingRegion` attribute (or 'content' by default').
Merge pull request #8 from trabian/feature/promised-views

Added BaseApplication with loading view