Better support for Wacom tablet

The Qt framework does not support all features of the Wacom tablets and does not provide any API to update its handling of the tablet at run-time if the tablet configuration change.

For example:

1. Qt assumes that the tablet is always mapped to all monitors. (It can be mapped to a single one or anything in between.)

2. Qt reads the characteristics and a subset of the configuration once at startup and cannot be told to re-read it later. (Currently, there are undocumented hacking way to modify the values cached by Qt about, for example, the size of the tablet, but this requires calling unprototyped functions returning private data structures that just happen to be visible at link time...) It would be better to provide a few function to at least update the data.

3. Qt only reads a subset of all possible configuration of a Wacom tablet. (It ignores twinview view at the tablet level, for example.)

4. Qt does not support all buttons on Wacom tablets (for example Intuos4) nor touch pads or touch rings.

5. Qt ignores that the X11 device event might report fewer axis than the full axis set. (IOW, Qt ignores the first_axis data member of the event.)