Add Push Notifications for activity

[thelooter]

Get notified when events happen in your project. This should be configurable as not to annoy users too much

[thelooter]

Suggested by @e3rd over at gitplus_for_gitlab

[thelooter]

This is a bit of a complex problem as this requires defining scopes of notifications that should be enabled or disabled as the user wishes. Ideally this could also be configured at a per project basis, but that most likely won't be in the initial implementation

[c33s]

support via unified push would be nice (https://ntfy.sh, https://unifiedpush.org/)

edit: added unified push url

[thelooter]

I think that this really could be helpful, I currently don't really have the time to tackle this on my own though. Currently I am barely able to maintain this project as is, so I need to really think about what I am working on.