Further improve the StocQt demo

- Display the price scale on y-axis, highest trade volume on x-axis
- Adjust grid size for the chart based on the active view
- Fix incorrect drawing of volume data
- Correctly scale the chart based on the price/volume ranges
- Align the volume graph to the price chart and improve its look
- Use Date.toDateString() instead of hardcoded month names
- Minor fixes to layout

Task-number: QTBUG-38254
Change-Id: I0e7ef18a152c7678371fb9c01f86d3d91a289472
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>
Reviewed-by: Niels Weber <niels.weber@digia.com>