TileConstants: replace BLBN, BLBNCN, BNCN constants with definitions

This will make it easier to find and replace uses of BULLBIT, BURNBIT, and
CONDBIT.
tiles.rc: annotate tiles with "noburn" if they are not combustible
tiles.rc: move BURNBIT knowledge from source code to tiles.rc
tiles.rc: annotate conductive tiles
graphics: high-color water
graphics: make a high-color DIRT tile image
graphics: use a transparent layer to implement wires
graphics: experiment with new forest graphics (work in progress)
graphics: more work on hi-color forest
graphics: experiment with an SVG wire tile
graphics: finish work on high-color forest
graphics: use an SVG-based police station
graphics: make SVG road tiles
tiles.rc: move CONDBIT knowledge from source code to tiles.rc
tiles.rc: use inheritance to define roads with traffic
graphics: SVG traffic (vertical and horizontal)
graphics: implement some curved traffic as SVG images
graphics: fix curved traffic SVG animation
graphics: finish SVG traffic for all curved roads
tile declarations: experimenting with new parser for tile declarations