Fix display none

Included in this PR are several small interface changes that Kyle and I made.

-In the case that no valid schedules are generated, tells the user with a new message (see pull request #50)
-Removes subnav buttons from view page in the case that no schedules are generated
-Fixes loading bar bug that shows part of the bar initially green
-Adds horizontal scrollbar to constraints added box
-Checks credit hours on input and terminates if wrong values are passed (issue #52)
-Loading bar updates periodically during schedule generation