wordsearch changes and tests

This started out as me just adding more unit tests.  I then realized that I was doing the wrong thing in the case where you spell the right word but keep going.  I refactored wordsearch so that instead of having a finish, we just run through all the steps, and then see if we match the search word.

It also turned out the drawMapTiles test wasn't really running properly, which led to a little more refactoring there.
It's the same thing as Maze.SQUARE_SIZE I just didn't want to have to require Maze to load WordSearch (in particular because that would require a circular dependency).  Other options would include making it a constant in some other file that both Maze and WordSearch load, or leaving it in Maze and having the unit test create a Maze global with this property.  The approach I took seemed easiest.