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/scenedit/scen.graphics.hpp

@@ -18,7 +18,7 @@ rectangle get_item_template_rect (short type_wanted);
 void draw_items();
 void force_tiny_redraw();
 void draw_one_terrain_spot (short i,short j,ter_num_t terrain_to_draw);
-void draw_one_tiny_terrain_spot (short i,short j,ter_num_t terrain_to_draw,short size);
+void draw_one_tiny_terrain_spot (short i,short j,ter_num_t terrain_to_draw,short size,bool road);
 rectangle get_template_rect (unsigned short type_wanted);
 void draw_frames();
 void place_location();
@@ -32,6 +32,7 @@ void make_field_type(short i,short j,eFieldType field_type);
 void take_field_type(short i,short j,eFieldType field_type);
 bool container_there(location l);
 bool is_spot(short i,short j);
+bool is_road(short i,short j);
 short string_length(char *str);
 rectangle get_custom_rect (short which_rect);
 void init_dialogs();