Improved failed handling code for NZBs and Torrents

Cleaned the code up and move some code into its own function where its more suited, also checks if the shows air-by-date now to determine proper passing of season info. Episodes are pre-determined ahead of time so that finding the release name is easier. Multiple snatches of the same release are now cleaned up properly so that old stale entries or messed up db files don't get in the way of this feature working properly.