Pull out logic for verifying submission into its own method.
Address issue #69 by warning if the list of submitted files does not include the main class.  For instance, if the student is submitting Project1, the Submit program will warn that Project1.java is not submitted.
Merge pull request #92 from DavidWhitlock/issue-69-warn-if-main-project-class-not-submitted

Warn if main project class not submitted.  To address issue #69, I added a warning to the Submit program that informs the submitted when they do not include the main class for the project. That is, if the student is submitting Project1 and does not submit Project1.java, an warning will be issued.