Added DupeKey/DupeScore for NZBGet 12+

https://github.com/mr-orange/Sick-Beard/pull/589
Now against pistachitos branch

This adds a DupeKey and DupeScore for NZBGet 12 and higher. This way NZBGet knows that different quality's are the same episode. With slow connections and multiple qualitys selected it's not uncommon that a higher quality is send to NZBGet before the lower is downloaded. With this change NZBGet won't download (or stop download) the lower quality download.

The generated DupeKey is: Sickbeard-TVDBID-Season.Episode
The generated Dupescore is: quality * 100 (+ 10 for proper)

This saves time and bandwidth. I'm using this mod now for months without a problem.

Old NZBGet version will still work since a version check will be done.