Include detailed information about course causing thrown exception in valid_credit_hour_input()
Whitespace cleanup for week class
Only add default constraint if corresponding course / instructor exists
Add global instructor list
Fix indentation in default constraints file
Merge branch 'period' of https://github.com/donnell74/CSC-450-Scheduler into period

# By kylenovak
# Via kylenovak
* 'period' of https://github.com/donnell74/CSC-450-Scheduler:
  Display info/error message a maximum of two times
  Prevent info message box from being displayed so many times