feat(rxStatusSvc): Wrapper for rxNotify.

This provides a wrapper around `rxNotify` in order to make the repetitive usage of `{ type: 'success' }` type options less necessary.

It only works with singular messages today; the feature provided by `rxPromiseNotifications` is not being wrapped.

Thanks to @chriscantu for the initial version of the awesome service provided for vcenter-ui.
Thanks to @parlarjb for updating it with awesome features that makes the service even more usable.
Is this line needed? `$scope.notify` should be undefined by default...