More Major Updates

This was a big one.  I changed the way problems were generated to make
the program more flexible... I now have an enum class just for problem
types.  This allows me to make a simple API for the review screen.  The
review screen simply prints out your quiz, whether the problem was
correct or incorrect with corresponding colors and a strikeout.  I also
made a class for stats tables so they would display more properly.  A
new bug has shown up after this, though.  The bottomPanel in GameScreen
disappears after the first round of problems and all the answers were
set to 0.  I don't get why quite yet.  This problem is due to be fixed
by at least Friday.