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/main_gui.cpp

@@ -200,7 +200,7 @@ void FixTitleGameZoom(int zoom_adjust)
 	UpdateViewportSizeZoom(vp);
 }
 
-static const struct NWidgetPart _nested_main_window_widgets[] = {
+static constexpr NWidgetPart _nested_main_window_widgets[] = {
 	NWidget(NWID_VIEWPORT, INVALID_COLOUR, WID_M_VIEWPORT), SetResize(1, 1),
 };