New impulse-based VelocityTracker strategy.

New velocity calculation strategy for VelocityTracker.
The strategy models the phone screen as a physical object
that gets pushed by the finger. Upon liftoff, the total
work done on the object (past 100ms of data and at most
20 most recent samples) is considered to be kinetic energy,
which gets converted into equivalent velocity.
Works well with "bad" data - unclean touch liftoff,
repeated coordinates. Time-shift invariant. Performance
otherwise similar to the current default strategy,
quadratic unweighted least squares.

Bug: 35412046
Test: Recorded bad scroll event on swordfish, this fixes the
fling in the wrong direction. Also tested common usecase
scenarios on sailfish, no regressions observed. Similar
velocity values to lsq2 strategy.

Change-Id: Ib439db0ce3b4fe84f59cf66683eae0b5df7776eb