larger map/tile changes

-You can now have multiple tiles on the same square
-You can set a 'type' of tile - solid, foreground, background
-spritegroups for each different type of tile, all things that need
updating that tick
-make_matrix is now only for making a quick background, and add_tile()
is for adding tiles on top
-to add - proper mapmaking from a file, level editing - but these are at
a later date once we've got collision sorted out :D