wacom: Add support for stylus and eraser pressure ranges
This re-groups the stylus configuration into a group for tip pressure, a group for eraser pressure (if applicable) and a group for the button configuration.
The pressure groups have the slider for the pressure feel and a new spin button for the minimum ("floor") and maximum ("ceiling") pressure in percent.
Closes #3088
cc @jimmac - this is Option 1 from #3088 (comment 2149847) because it's easy to implement and doesn't require custom widgets. The spacing is off though, not sure where to set this (and to what value).
