Update comment
Make TimeRange act more like a Range

Don't actually subclass it because it's dumb
Surveys know a Range of seconds to collect samples
Now we can schedule things in the future
Alias 'last' to 'end'
Find baseline times for scheduling questions
Fix a comment
Fix failing participant test

(Can't regen schedule days if they're already
there)
Clean up RandomNoReplacementRecordChooser

Also add (and test) a serialize_state method, for
Participant#question_chooser_state
Add Survey#question_chooser

This is chintzy but I want this API for later.
Add Participant#question_chooser_state
Make the chooser tolerant of serialization bull
Participants can now schedule questions.

WOO. FUCKING WOO.