Add persistence of active gestures. This needs an UGAIM update to work.

Active gestures are sent as part of the login-response. Added
fetchActiveGestures to SQLite and MySQL; added an empty one for MSSQL and
NHibernate. Using the empty ones won't cause errors, but doesn't provide
persistence either, of course.

OpenSim/Data/MSSQL/MSSQLInventoryData.cs

@@ -798,6 +798,11 @@ namespace OpenSim.Data.MSSQL
                 m_log.Error("[INVENTORY DB] Error deleting folder :" + e.Message);
             }
         }
+
+        public List<InventoryItemBase> fetchActiveGestures (UUID avatarID)
+        {
+            return null;
+        }
         #endregion
     }
 }