Implement front-end delay experiments

[drbenvincent]

• [x] new alternate constructor
• [x] new inter_reward_delay kwarg for the constructor.
• [x] Act on supplied inter_reward_delay values in generating design space
• [x] add to tests
• [x] update default DA and IRI values based on Green, Fristoe, & Myerson (1994)
• [ ] add to chooser.py and manually test
• [x] add plotting for front end delay experiments, assuming fixed reward ratio
• [ ] add a Jupiter notebook to explore front end delays

Reference

Green, L., Fristoe, N., & Myerson, J. (1994). Temporal discounting and preference reversals in choice between delayed outcomes. Psychonomic Bulletin & Review, 1(3), 383–389. http://doi.org/10.3758/BF03213979