[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/error_html_test.exs

@@ -1,5 +1,5 @@
 defmodule PinchflatWeb.ErrorHTMLTest do
-  use PinchflatWeb.ConnCase, async: true
+  use PinchflatWeb.ConnCase, async: false
 
   # Bring render_to_string/4 for testing custom views
   import Phoenix.Template