This adds the ability to filter user signup with a whitelist
instead of or in addition to a blacklist.

Fixes #817

add support for reading S3 protocol from ENV
also add S3_HOSTNAME in .env.production.sample

If an :original gets converted into another format, it would get saved as
original_filename *anyway*, so generating the extension is pointless and
yields bad results for when you change the style definition later. This way,
old gifs will still have correct URLs

work flawlessly was a nightmare). WARNING: This commit makes the web UI connect to the streaming API instead
of ActionCable like before. This means that if you are upgrading, you should set that up beforehand.

Do not require e-mail address changes to be re-confirmed, it's only trouble for no real benefit

for extremely wide monitors

Reflect "requested" relationship in API and UI
Reflect inability of private posts to be reblogged in the UI
Disable Webfinger for locked accounts

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)

can be processed separately