[Enhancement] Delete media after "x" days (#160)

* [Enhancement] Adds ability to stop media from re-downloading (#159)

* Added column

* Added methods for ignoring media items from future download

* Added new deletion options to controller and UI

* Added controller actions and UI for editing a media item

* Added column to sources

* Added retention period to form

* [WIP] getting retention methods in place

* Hooked up retention worker

* Added column and UI to prevent automatic deletion

* Docs

* Removed unused backfill worker

* Added edit links to media item tabs on source view

* Clarified form wording

* Form wording (again)

test/pinchflat/boot/data_backfill_worker_test.exs

@@ -1,46 +0,0 @@
-defmodule Pinchflat.Boot.DataBackfillWorkerTest do
-  use Pinchflat.DataCase
-
-  alias Pinchflat.Boot.DataBackfillWorker
-  alias Pinchflat.JobFixtures.TestJobWorker
-
-  describe "cancel_pending_backfill_jobs/0" do
-    test "cancels all pending backfill jobs" do
-      %{}
-      |> DataBackfillWorker.new()
-      |> Repo.insert_unique_job()
-
-      assert_enqueued(worker: DataBackfillWorker)
-
-      DataBackfillWorker.cancel_pending_backfill_jobs()
-
-      refute_enqueued(worker: DataBackfillWorker)
-    end
-
-    test "does not cancel jobs for other workers" do
-      %{id: 0}
-      |> TestJobWorker.new()
-      |> Repo.insert_unique_job()
-
-      assert_enqueued(worker: TestJobWorker)
-
-      DataBackfillWorker.cancel_pending_backfill_jobs()
-
-      assert_enqueued(worker: TestJobWorker)
-    end
-  end
-
-  describe "perform/1" do
-    setup do
-      DataBackfillWorker.cancel_pending_backfill_jobs()
-
-      :ok
-    end
-
-    test "reschedules itself once complete" do
-      perform_job(DataBackfillWorker, %{})
-
-      assert_enqueued(worker: DataBackfillWorker, scheduled_at: now_plus(60, :minutes))
-    end
-  end
-end