Speeds up loading for onsite classchange grid

Before the grid loads, some profile data for all the students is loaded.
This data is mostly used for the autocomplete box, and includes student
names and id numbers. However, the grades of all students was also being
precomputed, even though grade data is not needed until after a student
is selected. This query takes an incredibly long time for large
programs.

Increases the performance of the grid loading by moving the computation
of the students grade from students_status() to get_schedule_json(), the
latter of which is called for individual students only when that data is
needed.