wacom: rotate OLED labels on left-handed setups

If the tablet is set to left-handed mode, invert the labels so
they look natural with the tablet physically rotated. CW and CCW
modes are also taken into account, so text is always displayed
from top to bottom, even though rotated 90 degrees.

https://bugzilla.gnome.org/show_bug.cgi?id=709667
wacom: Update pad (O)LEDS when rotation gsetting changes

This is so labels are updated accordingly as soon as the setting
is changed.