Overview Chart on Trends view

.. updated the overview chart to support trend view and summarise
   a season or date range.

.. scope now meaningful in the item registry.

.. added a new TopNOverviewItem to view a ranked list of activities
   by metric.

.. updated sparkline to plot variable range (>30days)

.. sort and multisort datafilter functions adjusted as caused a
   SEGV during testing (sorry not in separate commit).

src/Gui/GcWindowRegistry.h

@@ -72,8 +72,8 @@ enum gcwinid {
         Python = 43,
         PythonSeason = 44,
         UserTrends=45,
-        UserAnalysis=46
-
+        UserAnalysis=46,
+        OverviewTrends=47
 };
 };
 typedef enum GcWindowTypes::gcwinid GcWinID;