Changed variable names to make more sense

xyCoordinates became pixelCoordinates
hexCoordinates became gridCoordinates
horizontal and vertical in hexCoordinates became x and y
gridCoordinates are now used to refer to the location of a particular hex in the board, and pixelCoordinates are now used to refer to a specific pixel on the screen.
Changed the getXYCoordinates function to be called getCenter - as that is what it does - finds the center of the hex.
Changed the arguments to the getCenter function - it doesn't need to be passed the x and y values of the coordinate seperately.