Push-notifications

[erlend-sh]

Want to align ourselves with this effort:

https://discourse.atprotocol.community/t/centralized-notifications-anyone-working-on-this/688?u=erlend.sh

[meri-leeworthy]

Repeating what I said elsewhere which is that I think cross-app notification routing is a good feature for power users to add on top of native push notifications. The bulk of the complexity is IMO in defining the UX (mostly done, I think) and computing them (app-specific) in the app-server