Issue 284: modify SickBeard to clean up and remove old episodes

Modified SB to support defining episode manage settings per show. User can choose to keep all, the current season, or a range of 1-10 episodes. When an episode is identified as stale it's status is set to ignored and all associated media is removed from the filesystem.

This first pass solution does not:

* alert notifiers of removed media
* remove any files generated by the metadata providers
* clean up the edit show template

Note: I do plan on addressing these issues in the future