Change Channel to Source (#12)

* Ensure channel detail lookup doesn't download the video - oops

* Ran the needful migrations for replacing channels with sources

* got media source test back working

* channel tasks test

* Media indexing worker test

* media tests

* Got all tests working except controller tests

* got all tests working

* Renamed Channel struct to Source

* renamed ChannelTasks

* More renaming; renamed channel details module

* Removed Channel yt-dlp module, instead throwing things in the VideoCollection module

* Renamed what looks like the last of the outstanding data

test/support/fixtures/tasks_fixtures.ex

@@ -14,7 +14,7 @@ defmodule Pinchflat.TasksFixtures do
     {:ok, task} =
       attrs
       |> Enum.into(%{
-        channel_id: MediaSourceFixtures.channel_fixture().id,
+        source_id: MediaSourceFixtures.source_fixture().id,
         job_id: JobFixtures.job_fixture().id
       })
       |> Pinchflat.Tasks.create_task()