Improve UX/discoverability of push notifications

[jeriox]

taken from #989:

• I don't think users dig the settings to enable notifications. I think we should ask them when installing the PWA or after signing up for the first time or smth like that.
• push notifications don't (always) use symbols or good deep links to be actionable... There are probably more features we aren't using.
  • clicking the push notification could lead to a web version of the full notification to read it. That's probably better then directly redirecting to the disposition view if the users didn't read the whole notification or could not, because it was too long