Organized images and improved game render functionality.
Organized the the images under different directories according
to the role they are playing in the application. Also fixed some
bugs related to images loading and initialization.
Implemented a new class named BorderPiece.js, that is used to
store the information about different pieces of the border and to
store the reference to the image to use. This allows to load the
image once and the use many times, without changing its attributes.