Refactored FullCalendar controller code

Optimized this messy code.  Also, fixed the issue where courses would
disappear when you add a class to the schedule (only affected the modal
view when building classes).

The other important usability change is the removal of the duplicate
course from the instructor’s schedule view when building classes.  This
was really confusing for uses because it statically displayed a
duplicate class for the current class.
New Feature: Added federal holidays & down days

We now have federal holiday and AETC down days built into FTSS and they
are automatically skipped by default when building classes.