* 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
* Add support for separate Redis for cache
CACHE_REDIS_URL to allow using a different Redis server for cache
purposes, with cache-specific configuration such as key eviction
* Fix code style issues
