Refactored some code to remove warnings in preparation for new code.
Refactored some duplicate code into a single method.
Broke up big method into smaller methods to make this code easier to work with.
Beginnings of a panel for entering letter grade ranges.
Got the grade ranges UI looking good enough.
Don't display grade ranges for "I" and "X" grades.
Display grade ranges from the grade book.
Save letter grade range information from GUI to grade book.
Display the max value to the left of the min value of a grade range so that it reads easier left-to-right.
Clear the min/max text fields before loading a grade book.  Since, at the moment, each grade book has default values for grade ranges, clearing the value might not make any difference.
Use GridBagLayout to make the grade ranges look nicer.
Merge pull request #90 from DavidWhitlock/compute-final-grade

Display and edit letter grade ranges in grade book GUI.  Added a new section to the "Class" tab of the Grade Book GUI that displays and edits the letter grade ranges for the grade book. Along the way, I refactored some of the GUI code to make it easier to read and leveraged some newer language features.