* Fix misuse of foreign_type
* Fix use of removed "add_template_helper"
* Use response.media_type instead of response.content_type in tests
* Fix CSV export controller test on Rails 6
Rails 6 sets a "filename*" field in the Content-Disposition header to
explicitly encode the filename as UTF-8.
This changes checks the first part of the Content-Disposition header so
it matches in both Rails 5 and Rails 6.
* Fix emoji formatting with Rails 6
* Make emoji output more idiomatic and robust
* Switch from redis-rails gem to built-in Rails redis cache storage
This change includes:
- Improve the spec coverage for incoming request to the webfinger action
- For requests without an accept header (ie, what a browser might look like),
return a JSON response.
- For requests with an explicit format of xml or json, return that format.
- For requests using an accept header, return that format.
Also adds failing spec showing webfinger does not return xml, which covers the
issue described in: https://github.com/tootsuite/mastodon/issues/1983
