GUI2: convert remaining uses of dialog_callback to std::bind

dialog_callback was designed to be passed where a void(widget&) function was expected.
It took the widget parameter, then found its dialog and window, and called the given
callback on that dialog object with the window as a parameter. I had left a few remaining
usecases for convenience, but it's not needed anymore.

* Faction Select: window parameter can be directly bound with std::ref
* Unit Create: window parameter not even needed, was only there to satisfy dialog_callback's
  signature.
* MP Create Game: window parameter needed, but I changed it to an in-function variable using
  modal_dialog::get_window. There's no window object to directly bind in the constructor, and
  using the actual callback widget's own get_window method just seems redundant.

src/gui/dialogs/multiplayer/faction_select.cpp

@@ -68,7 +68,7 @@ void faction_select::pre_show(window& window)
 	gender_toggle_.set_member_states("random");
 
 	gender_toggle_.set_callback_on_value_change(
-			dialog_callback<faction_select, &faction_select::on_gender_select>);
+		std::bind(&faction_select::on_gender_select, this, std::ref(window)));
 
 	//
 	// Set up leader menu button

src/gui/dialogs/multiplayer/mp_create_game.cpp

@@ -82,12 +82,12 @@ mp_create_game::mp_create_game(const config& cfg, saved_game& state, bool local_
 	, selected_game_index_(-1)
 	, selected_rfm_index_(-1)
 	, use_map_settings_(register_bool( "use_map_settings", true, prefs::use_map_settings, prefs::set_use_map_settings,
-		dialog_callback<mp_create_game, &mp_create_game::update_map_settings>))
+		std::bind(&mp_create_game::update_map_settings, this)))
 	, fog_(register_bool("fog", true, prefs::fog, prefs::set_fog))
 	, shroud_(register_bool("shroud", true, prefs::shroud, prefs::set_shroud))
 	, start_time_(register_bool("random_start_time", true, prefs::random_start_time, prefs::set_random_start_time))
 	, time_limit_(register_bool("time_limit", true, prefs::countdown, prefs::set_countdown,
-		dialog_callback<mp_create_game, &mp_create_game::update_map_settings>))
+		std::bind(&mp_create_game::update_map_settings, this)))
 	, shuffle_sides_(register_bool("shuffle_sides", true, prefs::shuffle_sides, prefs::set_shuffle_sides))
 	, observers_(register_bool("observers", true, prefs::allow_observers, prefs::set_allow_observers))
 	, registered_users_(register_bool("registered_users", true, prefs::registered_users_only, prefs::set_registered_users_only))
@@ -541,7 +541,7 @@ void mp_create_game::on_game_select(window& window)
 	options_manager_->update_game_options();
 
 	// Game settings
-	update_map_settings(window);
+	update_map_settings();
 }
 
 void mp_create_game::on_tab_select(window& window)
@@ -739,8 +739,10 @@ void mp_create_game::update_details(window& win)
 	}
 }
 
-void mp_create_game::update_map_settings(window& window)
+void mp_create_game::update_map_settings()
 {
+	window& window = *get_window();
+
 	if(config_engine_->force_lock_settings()) {
 		use_map_settings_->widget_set_enabled(window, false, false);
 		use_map_settings_->set_widget_value(window, true);

src/gui/dialogs/multiplayer/mp_create_game.hpp

@@ -136,7 +136,7 @@ private:
 	void show_description(window& window, const std::string& new_description);
 
 	void update_details(window& window);
-	void update_map_settings(window& window);
+	void update_map_settings();
 
 	/**
 	 * Dialog exit hook to bring up the difficulty dialog when starting a campaign.

src/gui/dialogs/unit_create.cpp

@@ -101,7 +101,7 @@ void unit_create::pre_show(window& window)
 	gender_toggle.set_member_states(last_gender);
 
 	gender_toggle.set_callback_on_value_change(
-			dialog_callback<unit_create, &unit_create::gender_toggle_callback>);
+		std::bind(&unit_create::gender_toggle_callback, this));
 
 	listbox& list = find_widget<listbox>(&window, "unit_type_list", false);
 
@@ -255,7 +255,7 @@ void unit_create::filter_text_changed(text_box_base* textbox, const std::string&
 	list.set_row_shown(show_items);
 }
 
-void unit_create::gender_toggle_callback(window&)
+void unit_create::gender_toggle_callback()
 {
 	gender_ = gender_toggle.get_active_member_value();
 

src/gui/dialogs/unit_create.hpp

@@ -76,7 +76,7 @@ private:
 	/** Callbacks */
 	void list_item_clicked(window& window);
 	void filter_text_changed(text_box_base* textbox, const std::string& text);
-	void gender_toggle_callback(window& window);
+	void gender_toggle_callback();
 
 	void update_displayed_type() const;