Updates lottery to use Django 1.4 bulk_create

This code change should produce significant speed boosts in the lottery
assignment controller.

Is untested, but should work correctly, as the given bulk_create
statement is syntactically equivalent to the original code (assuming I
wrote it correctly).

Resolves Github Issue #563.
Bring in recent local changes to lottery code

These were used for MIT Splash.  The code no longer assumes that the
number of timeslots is the same for each day when the program is
multiple days.  This requires making the lunch_by_day array into a list
of potentially different sized 1-D arrays, rather than a single 2-D array.
Make lottery tolerant of null graduation_year values in student profiles
Merge pull request #569 from learning-unlimited/lottery_bulk_create

Updates lottery to use Django 1.4 bulk_create