Fix display none

[CameronHKIng]

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

[kylenovak]

:+1:

[hana9235]

This works well if it's hit on the very first run. Everything works as it should and is displayed/hidden correctly. However, when the program is run successfully first, then conflicting constraints are added and it is re-run, I run into the following issues:

• the buttons on the view page are still displayed (for the first 5 invalid schedules)
• the message pops up and (mostly) covers the view screen; it could be like three pixels taller and it'd be less distracting. The way it is now, the blue days of the week bar at the top of the view schedule window can be seen above the message. (I know, that's nitpicky. If it can't be fixed because of Tkinter limitations, that's fine.)
• if the conflicting constraints are cleared and the program is run again, the new message that comes up over top of the schedule display does not go away.

For example (the schedules are invalid here, but I get the same screen after clearing bad constraints):

[CameronHKIng]

I must have been out of it when I was testing; I was trying to fix that problem with c2cdf0a. Thanks for pointing that out. I'll look into it.

[CameronHKIng]

@hana9235 @donnell74 @kylenovak I believe I fixed the issue; if you could look at it again, that would be great. Kyle also added a few new interface changes. They're in the list. The only thing I did not fix were the lines.

[hana9235]

Great job, looks good to me!

[kylenovak]

looks good.