Support Safari Push and Mobile Device Management

Rounding out support different types push notifications:

* Title, Action and URLArgs are for Safari Push notifications.
* MDM is for Mobile Device Management.

This just allows these types of notifications through, it doesn't ensure that they are fully valid. I'm doing validations in advance.
@bdotdub The thing is the json shouldn't include an empty "aps" node when using MDM.

Perhaps it makes more sense to check if aps is empty? Of course APS isn't just a string, so that's a deep check to ensure the entirety of APS is zero values.