* [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)
Kieran