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 that still true if you're using `_.merge` for all references to the objects (except for the clear status, which I assume won't be mutated)? Merge should return a new object, not a reference to the existing one.