Added additional priorities supported by SABnzbd.

From shypike:This is the (kind of weird) priority table:

TOP_PRIORITY = 2
HIGH_PRIORITY = 1
NORMAL_PRIORITY = 0
LOW_PRIORITY = -1
DEFAULT_PRIORITY = -100
PAUSED_PRIORITY = -2

-100 won't do a thing, since it means: whatever is default.

NzbDrone.Web/Models/DownloadSettingsModel.cs

@@ -96,6 +96,6 @@ namespace NzbDrone.Web.Models
             set;
         }
 
-        public SelectList PrioritySelectList = new SelectList(new string[] { "Low", "Normal", "High" });
+        public SelectList PrioritySelectList = new SelectList(new string[] { "Default", "Paused", "Low", "Normal", "High", "Top" });
     }
 }