Still check for S3_CLOUDFRONT_HOST for existing installs.

* Fix uncaching worker

* Revert to using Paperclip's filesystem backend instead of fog-local

fog-local has lots of concurrency issues, causing failure to delete files,
dangling file records, and spurious errors UncacheMediaWorker

* Update paperclip.rb

* Update .env.production.sample

* Update paperclip.rb

This reverts commit 40871caa4b.

* Revert "Bump version to 2.3.2rc1"

This reverts commit cdf8b92fea.

* Revert "Downgrade Dockerfile to Ruby 2.4.3 on Alpine 3.6 (#6806)"

This reverts commit 0074cad44f.

* Revert "Handle Mastodon::HostValidationError when pulling remoteable assets (#6782)"

This reverts commit 4a0a19fe54.

* Revert "Correct the reference to user's password in mastodon:add_user task (#6800)"

This reverts commit 338bff8b93.

* Revert "Upgrade Paperclip to version 6.0.0 (#6754)"

This reverts commit b88fcd53f7.

Keystone V2 is deprecated in favour of V3. This adds the necessary
connection parameters for establishing a V3 connection. Connections
to V2 endpoints are still possible and the configuration should
remain compatible.

This also introduces a SWIFT_REGION variable for multi-region
OpenStack environments and a SWIFT_CACHE_TTL that controls how long
tokens and other meta-data is cached for. Caching tokens avoids
rate-limiting errors that would result in media uploads becoming
unavailable during high load or when using tasks like
media:remove_remote. fog-openstack only supports token caching for
V3 endpoints, so a recommendation for using V3 was added.

* Fix #1642, fix #1912 - Previous change (#1718) did not modify how original file was saved on upload

* Fix for when file is missing

* Custom Paperclip path.

* Document PAPERCLIP_ROOT.

* Add PAPERCLIP_ROOT_URL (and rename PAPERCLIP_ROOT to PAPERCLIP_ROOT_PATH).

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

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)