Added virtual canvases, viewport for larger map, tmx json map loading, tileset painting, scrolling

Virtual canvases store the entire map. Viewports (or actually smaller
canvases) load partial content from the larger map. tmx json files
successfully load. Background images removed from html and js files, as
a few map functions now paints graphics from the tileset onto the
canvas. Static background images are no longer necessary and removed
from html and js. Scrolling implemented at player speed when player
nears left and right edges of screen.