Merge pull request #1 from RyanW117/master

I got rid of some imports that are not being used in the JavaMastersUI.
Merge pull request #2 from RyanW117/master

Added a Button import
Added HelpfulLinks class
Merge pull request #3 from EricSM/master

Added HelpfulLinks class
I changed the JavaMastersUI's Layout from GridLayout to Vertical Layout.
I also updated the NavigationMenu so that it is able to dropdown the
overviw, practice problems, and helpful links page and navigate to those
pages.
I changed the JavaMastersUI Layout from Grid to Vertical.  I made the
NavigationMenu have the drop down functionality.  And clicking on the
Overview, Practice Problems, and Helpful Links changes the centerPanel