Always use cumulative mode

The total motion of all active fingers is used for scrolling/cursor movement.

Signed-off-by: Morten Hustveit <morten.hustveit@gmail.com>
Ignore all motion 30ms after touching or filtering

The touch area sensing sometimes lags behind the centroid sensing, so this
dampening helps us pass the drumroll test.  We want the interval to be as short
as possible, and 30ms seems to work fine.  This is less than one animation
frame at 30 fps.

Signed-off-by: Morten Hustveit <morten.hustveit@gmail.com>