slightly optimized FanOutOnWriteService again

adjusted to allow choosing it, yet

FanOutOnWriteService. The only recipient-specific part on them
is reblogged/favourited. But since only newly created statuses
appear on them, it is safe to assume that both attributes would
be false

redis-backed "mentions" timeline as redundant (given notifications)

Fix #233, fix #268

Fix #289 - don't download avatar unless the URL is http/https
Fix #293 - reblog/reblogged is now boost/boosted

during Fan Out On Write to load less stuff into memory

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)