Tweak notification fetch frequency

[bmesuere]

Right now, we check for new notifications every 60 seconds even if the tab is in the background. This can be improved by only checking if the tab is visible and maybe adding some kind of backoff. The good new is that we have already implemented such logic in the auto_reload.ts file.

The reason for this is a substantial server load by the notification controller.
Last week, the notifications accounted for a third of the cpu time:

And 2/3 of the number of hits:

[bmesuere]

I thought some more about this. Since we load the notifications lazily, we always have an additional notifications hit for every page load. Simply being smarter about the refresh time would help but not a lot.

An alternative is a better cache system and/or keep the latest update time in local storage and don't fetch the notifications on every page load.