Reform scenario editor menu -> command mapping so that the non-platform-dependent code doesn't need to know where the menuitem is

src/tools/winutil.h

@@ -20,6 +20,7 @@ void makeFrontWindow(sf::Window& win);
 void setWindowFloating(sf::Window& win, bool floating);
 
 void init_fileio();
+void launchURL(std::string url);
 
 fs::path nav_get_party();
 fs::path nav_put_party(fs::path def = "");

src/tools/winutil.mac.mm

@@ -145,6 +145,10 @@ void beep() {
 	NSBeep();
 }
 
+void launchURL(std::string url) {
+	[[NSWorkspace sharedWorkspace] openURL:[NSURL URLWithString:[NSString stringWithCString:url.c_str() encoding:NSUTF8StringEncoding]]];
+}
+
 int getMenubarHeight() {
 	// Mac menubar isn't in the window, so we return 0 here.
 	return 0;

src/tools/winutil.win.cpp

@@ -213,6 +213,10 @@ void beep() {
 	MessageBeep(-1);
 }
 
+void launchURL(std::string url) {
+	ShellExecuteA(NULL, "open", url.c_str(), NULL, NULL, SW_SHOWNORMAL);
+}
+
 // TODO: Implement modal session.
 // It seems that Windows doesn't have anything similar to the Mac modal session, so I might have to somehow simulate it myself.
 void ModalSession::pumpEvents() {