W'bal y-axis consistency

.. in stack mode always start from min W'bal or 0, whichever
   is smaller. This makes it easier to identify when W'bal
   is (or is not) being consumed across rides.

src/IntervalTreeView.cpp

@@ -144,3 +144,37 @@ IntervalTreeView::mimeData (const QList<QTreeWidgetItem *> items) const
     return returning;
 }
 
+void 
+IntervalColorDelegate::paint(QPainter *painter, const QStyleOptionViewItem &option,
+               const QModelIndex &index) const 
+{
+    QStyledItemDelegate::paint(painter, option, index);
+
+    painter->save();
+
+    // Only do this on items !
+    if(index.isValid() && index.parent().isValid()) {
+
+        // extract the state of item
+        bool hover = option.state & QStyle::State_MouseOver;
+        bool selected = option.state & QStyle::State_Selected;
+        bool focus = option.state & QStyle::State_HasFocus;
+
+        // get the interval item a bit convoluted !
+        QTreeWidgetItem *item = tree->itemFromIndexPublic(index);
+        QVariant v =  item->data(0, Qt::UserRole);
+        IntervalItem *interval = v.isValid() ? static_cast<IntervalItem*>(v.value<void*>()) : NULL;
+
+        // rhs mark to show interval colour
+        if (!selected && !hover) {
+
+            // 7 pix wide mark on rhs
+            QRect high(option.rect.x()+option.rect.width() - 7, 
+                       option.rect.y(), 7, tree->rowHeightPublic(index));
+
+            // use the interval colour
+            painter->fillRect(high, interval->color);
+        }
+    }
+    painter->restore();
+}