Remove ColumnChooser "duplicates"

.. where metadata fields are actually for metric
   overrides we do not need to add to the list -
   since they are already there as metrics.

src/RideNavigator.cpp

@@ -1298,10 +1298,15 @@ ColumnChooser::ColumnChooser(QList<QString>&logicalHeadings)
     QList<QString> buttonNames = logicalHeadings;
     qSort(buttonNames.begin(), buttonNames.end(), insensitiveLessThan);
 
+    QString last;
     foreach (QString column, buttonNames) {
 
+        // ignore groupby
         if (column == "*") continue;
 
+        // ignore meta fields that are metrics or duplicates
+        if (column == last || column.contains("_")) continue;
+
         // setup button
         QPushButton *add = new QPushButton(column, this);
         add->setFont(small);
@@ -1310,6 +1315,10 @@ ColumnChooser::ColumnChooser(QList<QString>&logicalHeadings)
 
         connect(add, SIGNAL(pressed()), clicked, SLOT(map()));
         clicked->setMapping(add, column);
+
+        // for spotting duplicates
+        last = column;
+
     }
     scrollarea->setWidget(but);