Maintain ordering of classes in four year planner

[jreinstra]

Keep the ordering of the classes in each quarter in the four year planner. Likely will need to change how this data is stored in the DB.

[jreinstra]

Links:

• http://stackoverflow.com/questions/9602217/define-an-order-for-manytomanyfield-with-django
• https://docs.djangoproject.com/en/1.8/topics/db/models/#intermediary-manytomany