Several fixes for automatic trailer download, added Hd-trailer.net support

- Fixed: if download from scraped trailerURL failed, try using another scraped trailerURL for that movie (before: if download fails, give up!)
- Fixed: If global setting  "Delete existing trailers" is checked, Ember will now attempt to delete all trailers in movie folder before saving new one! (before: no trailer deleting, cluttering of different trailer files (A.C.O.D..2007.WEBRIP-trailer.mov, A.C.O.D..2007.WEBRIP-trailer.mp4, A.C.O.D..2007.WEBRIP-trailer.webm) in folder)
- Added: HD-trailer.net scraper
- Fixed: respect order of trailer modules
- Fixed: During automatic trailer scraping, only trailers which have string "trailer" in scraped trailer descriptions will be recognized - all other scraped results (like "making of") will be ignored. That should enhance scraping results.
- Changed: Removed module quality setting in Apple Trailer scraper module. Instead use only the one global setting. (IMDB/TMDB/HD-trailer also use the global setting, so its just more logical)