Added support for the 'Sensing Win7-TwoFinger' panel by GeneralTouch found on some tablets.

Because of conflicting VID/PID, this conflicts with previous support for some
single-touch panels by GeneralTouch
Signed-off-by: NBenjamin Tissoires <benjamin.tissoires@enac.fr>
Signed-off-by: NStéphane Chatty <chatty@enac.fr>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>