Delete media items (#20)

* Added method for deleting media files and their content

* Adds controllers and methods for deleting media and files

* Improved tmpfile setup and teardown for tests

* Actually got tmpfile cleanup running once per suite run

* Finally fixed flash messages

test/support/conn_case.ex

@@ -34,6 +34,7 @@ defmodule PinchflatWeb.ConnCase do
 
   setup tags do
     Pinchflat.DataCase.setup_sandbox(tags)
+    Pinchflat.DataCase.setup_temp_filepaths()
     {:ok, conn: Phoenix.ConnTest.build_conn()}
   end
 end