Add push notification

[strifel]

Add support for push notification.

Wouldn`t that be cool if you can receive a push notification when the Stundenpläne are online?

I think the recommended way is firebase.

[strifel]

To clarify this issue. This is only meant as cloud notification.

One human sends Push Notification to all users.

For other ideas see #12 and #11. Or create your own issue

[strifel]

After a bit more investigating. I think it is not possible (for us) to use firebase cloud messaging and own (on device) notifications.

We should probably either build up our own Notification System with our own API or cancel this issue.

So this issue is at least a lot postponed.

[strifel]

This could theoretically work with #12 if we implement it in our API.

E.g. Client -> "I want RPlan Updates" -> API Client -> Opens Channel -> API API -> "Here your Update" ->

This would be the best option I guess. Maybe even for #11. But I will implement #11 local based first.

For clarification: This issue is (still) only for user messaging. Like: Client -> Opens Channel -> API Admin -> Notification "Test" -> API API -> Notification "Test" -> Client

[strifel]

Wir machen das jetzt mit Firebase. Hierfür muss die Implementation erfolgen

[kagOT]

Firebase

[strifel]

Hierfür wird noch auf die API gewartet. Grundsätzlich sind Notifications implementiert