Quality check fix

Hi ! Thanks a lot for this fork, I got it on your topic on binnews.

The changes I made are mainly related to the quality restriction which wasn't working; I had set 720p WEB-DL and it downloaded HDTV episodes.
The quality check you were doing manually actually exists in the base Sick Beard code, the function is [Quality.nameQuality](https://github.com/brainlesscurls/Sick-Beard/blob/bef73cdf431c4499e25ffcf62fffae543754e7eb/sickbeard/common.py#L138-L180).
I also refactored some of the code (not much), I hope you don't mind.