[Enhancement] Allow redownloading of files for existing media items (#239)

* Added ability to specify overwrite behaviour when downloading media

* Added helper for redownloading media items

* renamed media redownload worker to disambiguate it from similarly named methods

* Added new redownload option to source actions dropdown

* Refactored MediaQuery to use a __using__ macro

* docs

config/config.exs

@@ -54,7 +54,7 @@ config :pinchflat, Oban,
     {Oban.Plugins.Cron,
      crontab: [
        {"0 1 * * *", Pinchflat.Downloading.MediaRetentionWorker},
-       {"0 2 * * *", Pinchflat.Downloading.MediaRedownloadWorker}
+       {"0 2 * * *", Pinchflat.Downloading.MediaQualityUpgradeWorker}
      ]}
   ],
   # TODO: consider making this an env var or something?