automatically generate archive coverage page

with T1251 out of the door, we're left with this to do (in the long term):

• export the list of crawled places from the DB that contains the scheduling tasks. This probably requires both distinguishing listing tasks from others and adding metadata such as where to find the relevant logo, for places for which we want to have a logo. (I'm assuming this would be easier/better than making the webapp access directly the scheduler DB.)
• make the web app access that information to dynamically generate the coverage representation

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Migrated from T1266 (view on Phabricator)