Added quick map
Replaced quick map with tiny map

The quick map was basically a mask of the orthographic map.

The tiny map is the same thing but at chunk scale instead of block
scale: it simply renders a white pixel for every chunk that exists in
the world.
Fix one-character bug

In isometric view, partially obscured blocks with different colours on
top and left sides were being drawn with the top colour on the left
side. Fixed.