Merge branch 'master' into jgrpp

# Conflicts:
#	src/airport_gui.cpp
#	src/build_vehicle_gui.cpp
#	src/direction_type.h
#	src/gfx_type.h
#	src/group_gui.cpp
#	src/misc_gui.cpp
#	src/rail_gui.cpp
#	src/road_gui.cpp
#	src/signs_gui.cpp
#	src/slope_func.h
#	src/smallmap_gui.cpp
#	src/terraform_gui.cpp
#	src/toolbar_gui.cpp
#	src/town_gui.cpp
#	src/town_type.h
#	src/vehicle_type.h
#	src/widget_type.h

src/gfx_type.h

@@ -249,6 +249,7 @@ enum Colours : uint8_t {
 	INVALID_COLOUR = 0xFF,
 };
 template <> struct EnumPropsT<Colours> : MakeEnumPropsT<Colours, byte, COLOUR_BEGIN, COLOUR_END, INVALID_COLOUR, 8> {};
+DECLARE_ENUM_AS_ADDABLE(Colours)
 
 /** Colour of the strings, see _string_colourmap in table/string_colours.h or docs/ottd-colourtext-palette.png */
 enum TextColour {