[Bugfix] Improve OPML route security (#535)

* WIP - moved plugs; set up a new token-protected route plug

* Added a route_token column to settings model

* Hooked up token_protected_route plug to database

* Hooked up new OPML route to UI; turned RSS and OPML feed buttons into links

* Docs, tests

* Added a note about the phoenix bug

lib/pinchflat/settings/setting.ex

@@ -31,6 +31,7 @@ defmodule Pinchflat.Settings.Setting do
     field :apprise_version, :string
     field :apprise_server, :string
     field :youtube_api_key, :string
+    field :route_token, :string
 
     field :video_codec_preference, :string
     field :audio_codec_preference, :string