Add touchscreen_feedback tool for generating touchscreen logs

This adds a script similar to "tpcontrol log" to generate logs of
touchscreen input events.

BUG=chrome-os-partner:11604
TEST=run feedback on link, verified logs present

Change-Id: I5e2661f15a8004bd8336d83219f8387868ea0664
Reviewed-on: https://gerrit.chromium.org/gerrit/30015
Reviewed-by: Andrew de los Reyes <adlr@chromium.org>
Commit-Ready: Michael Spang <spang@chromium.org>
Tested-by: Michael Spang <spang@chromium.org>