Fix #205, fix #156, fix #124

for avatars/headers, resize avatars down to 120x120 instead of 300x300. Set cache headers on S3 stuff, also
make it private (aka only accessible via expiring links to prevent hotlinking)

then adjust to failure later if the request fails

skip ActionCable for follow/unfollow/block events, instead clear UI from
blocked account's posts instantly if block request succeeds. Add forgotten
i18n for sensitive content

before loading new one, cache notifications API, fix missing follow button
on public profiles

status clickable (this also fixes multiple dropdown being openable at the same
time)

on scrollable areas

all statuses/accounts to assemble, but at least lists don't have to be
re-rendered all the time now. Also add "mention" dropdown option

Also fix reloading of timelines after merge-type events