Implemented gui-less mp_connect for sp

Also, made sides with blank controllers default to ai in sp.

src/multiplayer.cpp

@@ -489,6 +489,7 @@ static bool enter_connect_mode(game_display& disp, const config& game_config,
 	gamelist.clear();
 	statistics::fresh_stats();
 
+	if (state.classification().campaign_type == game_classification::MULTIPLAYER)
 	{
 		mp::connect_engine_ptr connect_engine(new mp::connect_engine(state, local_players_only, true));
 		mp::connect ui(disp, state.mp_settings().name, game_config, gamechat, gamelist,
@@ -502,6 +503,11 @@ static bool enter_connect_mode(game_display& disp, const config& game_config,
 		if (res == mp::ui::PLAY) {
 			ui.start_game();
 		}
+	} // end connect_engine_ptr scope
+	else {
+		mp::connect_engine engine(state, local_players_only, true);
+		engine.start_game();
+		res = mp::ui::PLAY;
 	}
 
 	switch (res) {

src/multiplayer_connect_engine.cpp

@@ -856,6 +856,7 @@ side_engine::side_engine(const config& cfg, connect_engine& parent_engine,
 	// Tweak the controllers.
 	if (cfg_["controller"] == "human_ai" ||
 		cfg_["controller"] == "network_ai" ||
+		(parent_.state_.classification().campaign_type == game_classification::SCENARIO && cfg_["controller"].blank()) ||
 		(cfg_["controller"] == "network" &&  !allow_player_ && parent_.params_.saved_game)) { //this is a workaround for bug #21797
 
 		cfg_["controller"] = "ai";