Gzip Rails responses by default (#495)

Gzipping responses trades some server and browser CPU for less data over
the network. This is particularly helpful for browsers on unstable or
slow Internet connections.

Closes #418

variants/backend-base/config/application.rb

@@ -30,5 +30,8 @@
     config.active_record.encryption.key_derivation_salt = Rails.application.secrets.active_record_encryption_key_derivation_salt
 
     config.action_dispatch.default_headers["X-Frame-Options"] = "DENY"
+
+    # gzip Rails responses to help browsers on slow network connections.
+    config.middleware.use Rack::Deflater
   RUBY
 end