Push Notifications with Pushover

@Chroma you can definitely use it either way - I have done both. If you want to offer notifications to your users you collect their token and secret and store them in the database, then send using those credentials instead of your system config. Pushover also offers bulk license purchases so you can buy a pack and assign tokens that you distribute to your users, rather then making them set it up themselves.

@marco thanks for the feedback! This is actually a port from my CI3 Pushover Helper. It was much more basic but I used it pretty heavily in CI3 so I’m glad to have this ready for 4 now