Add "include rests" Setting for WorkflowManager

Working toward issue #267, this setting will cause the vertical intervals
to include 'Rest' tokens, which is the current behaviour.

The new default behaviour will be to omit intervals that include or are
'Rest' tokens.
"Intervals" Experiment in WorkflowManager Heeds "Include Rests" Setting

And there's a test for it, too. Well, two tests, I guess.
Interval N-Grams Experiments Heed "include rests" Setting

With modified tests too!
Add Integration Test for Interval N-Grams (Not) Having Rests

(it's for the new "include rests" setting in the WorkflowManager)
Add Integration Test for Intervals (Not) Having Rests

(it's for the new "include rests" setting in the WorkflowManager)

Closes #267