Make roads an overlay instead of a terrain trim type

Game:
- Roads now show on the automap again!
- Possible fix for undetected issue in displaying outdoor special spots
- Road conversion code for legacy scenarios now applied in towns too

Editor:
- New tool for placing roads, works the same as special dots
- Roads appear at all zoom levels

Other:
- Removed all terrain graphics that used the small road dot, replacing them with blank (white) space
- Make obvious out-of-bounds array accesses an error in the project settings

src/boe.graphics.hpp

@@ -39,7 +39,6 @@ void put_text_bar(std::string str);
 void draw_terrain(short	mode = 0);
 void place_trim(short q,short r,location where,ter_num_t ter_type);
 void draw_trim(short q,short r,short which_trim,short which_mode);
-bool extend_road_terrain(ter_num_t ter);
 void place_road(short q,short r,location where,bool here);
 void draw_rest_screen();
 void boom_space(location where,short mode,short type,short damage,short sound);