Add new signal type: no-entry signal

This is only passable in one direction, but does not have a signal
or show an aspect in the opposite direction

Add a setting for whether this is shown in the signal UI.
Off by default.

src/settings_gui.cpp

@@ -1816,6 +1816,7 @@ static SettingsContainer &GetSettingsTree()
 			SettingsPage *advsig = interface->Add(new SettingsPage(STR_CONFIG_SETTING_INTERFACE_ADV_SIGNALS));
 			{
 				advsig->Add(new SettingEntry("gui.show_progsig_ui"));
+				advsig->Add(new SettingEntry("gui.show_noentrysig_ui"));
 				advsig->Add(new SettingEntry("gui.show_adv_tracerestrict_features"));
 			}