since that is only ever called in the background

Closes: #345

who don't follow them

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)

(without avatar). Also improved search position of exact matches

from accounts/tags because it's a terribly inefficient way to paginate
large sets of data

Fix #233, fix #268

by updating it at least every 24h if the user visits the site