Parallelize motion model update

[nahueespinosa]

This patch parallelizes the motion model update using standard C++ execution policies.

Particles: 2000
Points: 1080

	Sequential Duration [ms]	Parallel Duration [ms]	Speed up
Motion update	10.0660	1.2060	8.346600332
Sensor update	15.4800 *	15.2250	1.016748768
Resampling	11.5730	11.6670	0.9919430873
Total	37.1190	28.0980	1.321054879

*The sensor update is parallelized in both columns.

Related to #3.

[nahueespinosa]

With low particle counts, the overhead of spinning multiple threads becomes significant, especially on the motion update. However, we still see improvements in execution time:

Particles: 100
Points: 1080

	Sequential Duration [ms]	Parallel Duration [ms]	Speed up
Motion update	0.5750	0.2330	2.467811159
Sensor update	7.7610	1.6820	4.614149822
Resampling	0.6920	0.7390	0.9364005413
Total	9.0280	2.6540	3.401657875