Create metrics for evaluating Layer 4 sensorimotor inference

Fixes https://github.com/numenta/nupic.research/issues/13.
Builds on https://github.com/numenta/nupic.research/pull/30.
Depends on https://github.com/numenta/nupic/pull/1346.

cc: @subutai 
For posterity: We'll keep this metric, since it's useful for sensorimotor temporal memory, but document that it's not good for high-order sequence memory. We'll add a better metric for that in the future