added option to return an exclusivegroup from egid

Svelto.ECS/EGID.cs

@@ -13,9 +13,9 @@ namespace Svelto.ECS
             get { return (int) (_GID & 0xFFFFFFFF); }
         }
         
-        public int groupID
+        public ExclusiveGroup.ExclusiveGroupStruct groupID
         {
-            get { return (int) (_GID >> 32); }
+            get { return new ExclusiveGroup.ExclusiveGroupStruct((int) (_GID >> 32)); }
         }
 
         public static bool operator ==(EGID obj1, EGID obj2)

Svelto.ECS/ExclusiveGroups.cs

@@ -100,6 +100,11 @@ namespace Svelto.ECS
                 DBC.ECS.Check.Require(_globalId + range < ushort.MaxValue, "too many exclusive groups created");
                 _globalId += range;
             }
+            
+            internal ExclusiveGroupStruct(int groupID)
+            {
+                _id = groupID;
+            }
 
             public static implicit operator int(ExclusiveGroupStruct groupStruct)
             {