Refactored Code

Added a bunch of new classes (all .js) and moved code from Main.js to
them

(Button, Constants, Difficulty, Game, Gun, Images, Inventory, Keyboard,
Lives, Menu, Mouse, Multiplier, Statistics, Text, Util)

Made the "constructors" more java like (instead of Bubble(I), it is
Bubble(speed, hitsReq, x, y, image, points, weapon) )