Added a few images for demo purposes

The plan is to draw the blank domino and draw the appropriate image on
top for the domino numbers.
Added blank domino
index_3D.html now opens dominosGame_3D.js instead
Added game loop

Screen is redrawn 60 times per second. Draw all objects in the draw
function and put all updates in the update function. Updates are for
things such as checking timers, updating object positions.