Cookie auth (#116)

* Added new extras directory

* Automatically create cookie file on boot

* Added cookie file option to DL option builder

* Put cookie auth in correct spot

* Updated Docs

* Removed useless setter for config path

lib/pinchflat/release.ex

@@ -30,6 +30,7 @@ defmodule Pinchflat.Release do
       "/downloads",
       Application.get_env(:pinchflat, :media_directory),
       Application.get_env(:pinchflat, :tmpfile_directory),
+      Application.get_env(:pinchflat, :extras_directory),
       Application.get_env(:pinchflat, :metadata_directory)
     ]