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.
Looking into the usage of the `_.merge()`, `_.defaults()`, `_.whatever()` makes my head hurt. I sincerely am beginning to hate all these utility functions because they have side effects that the name doesn't suggest (even if they are documented, it doesn't make the utility less crappy).

In this case, apparently `_.merge()` merges into the first argument, and also returns the merged object. I tested this in console:
```javascript
> var a = {"a": 1}, b = {"b": 2}, c = {"c": 3}
> var d = _.merge(a, b)
> d
Object {a: 1, b: 2}
> d.a = 3 // this shouldn't modify the variable 'a', just the property 'a' on 'd'
> a
Object {a: 3, b: 2} // and yet it does
> b
Object {b: 2}
```

Also, I just realized I didn't address why we didn't use `_.defaults()`. `_.defaults()` only overrides the `undefined` keys on the left hand object; in our case we wanted to override the keys entirely if the user wanted to (which `_.merge()` seems to do). We didn't think it also modified the left hand object in place, but that appears to be the case from the observation above.