Changes to dojo, student, dojo_student

All dojo and dojo_student tests pass.  (Look at the git commit notes to see what was changed.)  Two keys ideas to remember:
1) Given the callbacks and rollbacks, use .delete rather than .destroy when removing contexts (the delete method gets rid of the data without calling the callback).
2) .build creates the value in memory but not in the database and thus the object built has no idea at the time.  Use .create if you want to actually add the data to the system.

There are no errors in student tests, but lots of failures because the order is not what is expected.  Not that the failures are corrected, see if you can solve the remaining order issues yourself. (But let me know if you need assistance.)