Fetching atom extracted from FetchRemoteAccountService and FetchRemoteStatusService
into FetchAtomService. Mentions of the constant "http://activityschema.org/collection/public"
skipped as it's not a real URL/user.

as well as formatting of content

in the pool, adding a throttle of 60rpm per IP, adding mini profiler, adding
admin status to users

and atom feed generation to some extent, as well as the way mentions are
stored

simplify FanOutOnWriteService, add /api/accounts/lookup method

fix tests (the recorded Salmon fixture expects LOCAL_DOMAIN to be something
specific unfortunately)