Add setting for alternative linkgraph overlay colour schemes

src/settings.cpp

@@ -1296,6 +1296,12 @@ static bool ViewportMapShowTunnelModeChanged(int32 p1)
 	return RedrawScreen(p1);
 }
 
+static bool UpdateLinkgraphColours(int32 p1)
+{
+	BuildLinkStatsLegend();
+	return RedrawScreen(p1);
+}
+
 /** Checks if any settings are set to incorrect values, and sets them to correct values in that case. */
 static void ValidateSettings()
 {