[Enhancement] Allow forcing a refresh of source metadata (#194)

* Stopped sources from fetching metadata on every update

* Added action button to force a metadata refresh

lib/pinchflat_web/router.ex

@@ -35,6 +35,7 @@ defmodule PinchflatWeb.Router do
     resources "/sources", Sources.SourceController do
       post "/force_download", Sources.SourceController, :force_download
       post "/force_index", Sources.SourceController, :force_index
+      post "/force_metadata_refresh", Sources.SourceController, :force_metadata_refresh
 
       resources "/media", MediaItems.MediaItemController, only: [:show, :edit, :update, :delete] do
         post "/force_download", MediaItems.MediaItemController, :force_download