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.Core/Model/SabnzbdPriorityType.cs

@@ -2,8 +2,11 @@
 {
     public enum SabnzbdPriorityType
     {
+        Default = -100,
+        Paused = -2,
         Low = -1,
         Normal = 0,
-        High = 1
+        High = 1,
+        Top = 2
     }
 }