Statuschecking for NZBGet

Added status checking for NZBGet. With this implementation all that is
required is a postprocessing script that extracts the release to the CPS
download folder.
added removeFailed to NZBGet provider
added delete_failed option to NZBGet provider
Made NZBGet compatible with #1511
Merge remote-tracking branch 'origin/develop_nzbget' into develop_dwnldid
No need for unicode