Add a location picker for selecting a location in a town or outdoor sector.

It's currently used in special node editing and in advanced town details.

src/scenedit/SConscript

@@ -8,6 +8,7 @@ scened_sources = Split("""
 	scen.fileio.cpp
 	scen.graphics.cpp
 	scen.keydlgs.cpp
+	scen.locpicker.cpp
 	scen.main.cpp
 	scen.townout.cpp
 	../view_dialogs.cpp
@@ -49,4 +50,4 @@ else:
 
 env.Package(scened, install_dir, scened_info)
 if debug_symbols is not None:
-	env.Install(install_dir, debug_symbols)
+	env.Install(install_dir, debug_symbols)