New motion threshold factor - speed feature.

Added a speed feature that focuses only on thresholds
for new motion modes.

Moved sf->comp_inter_joint_search_thresh into speed
1.  This has ~+0.4% impact on quality at speed 0 as
our quality reference baseline.

Slight adjustment to baseline thresholds.

Change-Id: I7ebf104f1fe29af77ed4837b2e84be065621bbe5