Updated calibration dialog.

- New: flipping and rotating axes, pixel size hint, coordinates offset.
- Improved: using numeric box instead of text box to support mouse scroll to change the numbers.
- Plus: added a menu in the coordinate system drawing to re-align it with the grid.
Pixel size can be thought of as the error bar at the center of the grid. If the digitization is off by one pixel this is how much it is off in real world units. (in pixels of the original video, not screen pixels, always good to zoom in).
No special treatment for tracking. The offset is just added at the end so it should work as before. I don't think tracking both the coordinate system and the calibration grid is a realistic scenario so until someone comes with a real use-case it will just keep giving precedence to the grid. We'll see later how that works with camera motion compensation.
Known limitation: The scatter plot diagram is showing the axes un-flipped.
