Add web notification integration

[MTGPROD]

Describe the new feature:

Just implement the notifications when a friend is online or when you receive a message etc. (even when your beatmap being ranked or something like that can be cool)

Proposal designs of the feature:

[thenerdie]

Yes, this is one of the things that they are going to add soon (likely)

[peppy]

This is quite a large task which is already planned but has no ETA nor ongoing work.

[MTGPROD]

You can take advantage of the new integration for notifications to set up this system. (Unless the bancho API doesn't allow it yet)