Add sequence metrics to TemporalMemoryInspectMixin

Fixes https://github.com/numenta/nupic/issues/1329.
Builds on https://github.com/numenta/nupic/pull/1338.

@subutai 
Hmmm. This function is really just a convenience method only used in this inspect class (for now). It's not used in the algorithm. Do you think I should put it in the `Connections` object anyway? I'm really not sure either way.