removing web app capability from non-webapp pages

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)

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

as well as formatting of content

(But there are no Atom feed pagination elements yet)

simplify FanOutOnWriteService, add /api/accounts/lookup method

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