Recent updates list

[kohlhase]

We should have a functionality that lists recent updates.

• "Archives Updates" For the moment, we can just link to https://gl.mathhub.info/, which shows the archives with changes (youngest first)
• "Activity", can link to https://gl.mathhub.info/dashboard/activity
• ... there must be more ...

I guess we want a drop-down for the "news" (like in "help") that has the current /News as "Announcements" and the other two as (lower) subfields.

Eventually (see #61), we want a native frontend for these with data supplied by the inventory (see #54).