[Enhancement] Custom media lifecycle scripts (#219)

* Namespaced notification modules under lifecycle

* Added a JSON encoder for all the main model types

* Added startup task to create user script file

* Hook up user script event to media download

* Hooked up media deletion user script

* Added jq to docker deps

* Updated README

test/pinchflat_web/controllers/source_controller_test.exs

@@ -145,6 +145,12 @@ defmodule PinchflatWeb.SourceControllerTest do
   describe "delete source when deleting the records and files" do
     setup [:create_source]
 
+    setup do
+      stub(UserScriptRunnerMock, :run, fn _event_type, _data -> :ok end)
+
+      :ok
+    end
+
     test "deletes chosen source and media_items", %{conn: conn, source: source, media_item: media_item} do
       delete(conn, ~p"/sources/#{source}?delete_files=true")