Work on issue #2144454: Inconsistent swipes...

This introduces some hacks in the framework to try to clean up the
data we are getting from the touch screen.  There are two main things
being done here:

1. Look for changes in position that are unreasonably large, and
ignore them.  This is intended to eliminate the spurious jumps that
often happen when releasing.

2. Add some simple adaptive averaging of the touch data.  If the
difference between the last and next point is large enough, we
disable the averaging; otherwise we average up to the last 5 points.
The goal is to get rid of the noise of small movements so that things
like taps don't look like short flings, while still responding quickly
to rapid movement.

For averaging pressure, we also weight each averaged coordinate by
the reported pressure at that point.  This is intended to keep the
coordinates closer together during a release, when the pressure is
going down and the accuracy decreasing.  It may also result in some
other interesting artifacts, but hopefully nothing problematic.

Change-Id: I1369e9ab015c406946a45c2d72547da9c604178f