[Enhancement] Ignore media based on user scripts (#330)

* Integrated pre-download callback for media items

* Refactored existing tests

* Docs, etc

test/pinchflat_web/controllers/media_profile_controller_test.exs

@@ -137,7 +137,7 @@ defmodule PinchflatWeb.MediaProfileControllerTest do
     setup [:create_media_profile]
 
     setup do
-      stub(UserScriptRunnerMock, :run, fn _event_type, _data -> :ok end)
+      stub(UserScriptRunnerMock, :run, fn _event_type, _data -> {:ok, "", 0} end)
 
       :ok
     end