mp method selection: improve accessibility

tab ordering has been added to the username textbox and the list of methods.
this serves two purposes:
1. the listbox is initially selected, so the user can select entries using keyboard.
2. navigation between the listbox and the username textbox can be done using TAB.

additionally,
3. the message and control layout has been tweaked to hopefully make it a bit user friendly.
4. the last selected method is remembered via a preference key.
5. a [X] button has been added on top-right so that the window can be
   closed via mouse. (previously, it was only possible with the keyboard
   Esc option or by clicking on one of the methods.)

data/gui/themes/default/window/mp_method_selection.cfg

@@ -5,7 +5,7 @@
 
 [window]
 	id = "mp_method_selection"
-	description = "Language selection dialog."
+	description = "Multiplayer playing mode selection dialog."
 
 	[resolution]
 		definition = "default"
@@ -39,6 +39,10 @@
 			[row]
 				grow_factor = 0
 
+				[column]
+					horizontal_grow = true
+					[grid]
+						[row]
 							[column]
 								grow_factor = 1
 
@@ -50,7 +54,17 @@
 									definition = "title"
 									label = _ "Multiplayer"
 								[/label]
+							[/column]
+							[column]
+								horizontal_alignment = "right"
 
+								[button]
+									id = "cancel"
+									definition = "close"
+								[/button]
+							[/column]
+						[/row]
+					[/grid]
 				[/column]
 
 			[/row]

src/gui/dialogs/multiplayer/mp_method_selection.cpp

@@ -22,7 +22,6 @@
 #include "gui/widgets/button.hpp"
 #include "gui/widgets/listbox.hpp"
 #include "gui/widgets/text_box.hpp"
-#include "gui/widgets/window.hpp"
 #include "preferences/preferences.hpp"
 
 namespace gui2::dialogs
@@ -30,20 +29,20 @@ namespace gui2::dialogs
 
 REGISTER_DIALOG(mp_method_selection)
 
+/** Link to the wesnoth forum account registration page */
 static const std::string forum_registration_url = "https://forums.wesnoth.org/ucp.php?mode=register";
 
 void mp_method_selection::pre_show()
 {
-	user_name_ = prefs::get().login();
-
 	text_box* user_widget = find_widget<text_box>("user_name", false, true);
-	user_widget->set_value(user_name_);
+	user_widget->set_value(prefs::get().login());
 	user_widget->set_maximum_length(mp::max_login_size);
 
-	keyboard_capture(user_widget);
-
 	listbox* list = find_widget<listbox>("method_list", false, true);
-	add_to_keyboard_chain(list);
+	list->select_row(prefs::get().mp_connect_type());
+
+	add_to_tab_order(list);
+	add_to_tab_order(user_widget);
 
 	connect_signal_mouse_left_click(find_widget<button>("register"),
 		std::bind(&desktop::open_object, forum_registration_url));
@@ -51,16 +50,18 @@ void mp_method_selection::pre_show()
 
 void mp_method_selection::post_show()
 {
-	if(get_retval() == retval::OK) {
+	prefs::get().set_mp_connect_type(find_widget<listbox>("method_list").get_selected_row());
-		listbox& list = find_widget<listbox>("method_list");
-		choice_ = static_cast<choice>(list.get_selected_row());
 
+	if(get_retval() == retval::OK) {
 		text_box& user_widget = find_widget<text_box>("user_name");
 		user_widget.save_to_history();
-
+		prefs::get().set_login(user_widget.get_value());
-		user_name_ = user_widget.get_value();
-		prefs::get().set_login(user_name_);
 	}
 }
 
+mp_method_selection::choice mp_method_selection::get_choice() const
+{
+	return static_cast<choice>(prefs::get().mp_connect_type());
+}
+
 } // namespace dialogs

src/gui/dialogs/multiplayer/mp_method_selection.hpp

@@ -27,27 +27,13 @@ public:
 	enum class choice { JOIN = 0, CONNECT, HOST, LOCAL };
 
 	mp_method_selection()
-		: modal_dialog(window_id()) , user_name_(), choice_()
+		: modal_dialog(window_id())
 	{
 	}
 
-	const std::string& user_name() const
+	choice get_choice() const;
-	{
-		return user_name_;
-	}
-
-	choice get_choice() const
-	{
-		return choice_;
-	}
 
 private:
-	/** The name to use on the MP server. */
-	std::string user_name_;
-
-	/** The selected method to `connect' to the MP server. */
-	choice choice_;
-
 	virtual const std::string& window_id() const override;
 
 	virtual void pre_show() override;

src/preferences/preferences.hpp

@@ -551,6 +551,7 @@ public:
 	PREF_GETTER_SETTER(mp_era, std::string, std::string(""))
 	PREF_GETTER_SETTER(mp_level, std::string, std::string(""))
 	PREF_GETTER_SETTER(mp_level_type, int, 0)
+	PREF_GETTER_SETTER(mp_connect_type, int, 0)
 	PREF_GETTER_SETTER(skip_ai_moves, bool, false)
 	PREF_GETTER_SETTER(save_replays, bool, true)
 	PREF_GETTER_SETTER(delete_saves, bool, false)
@@ -752,6 +753,7 @@ private:
 		prefs_list::mp_countdown_turn_bonus,
 		prefs_list::mp_fog,
 		prefs_list::mp_level_type,
+		prefs_list::mp_connect_type,
 		prefs_list::mp_random_start_time,
 		prefs_list::mp_server_warning_disabled,
 		prefs_list::mp_shroud,

src/preferences/preferences_list.hpp

@@ -176,6 +176,8 @@ struct preferences_list_defines
 	ADDPREF(mp_level)
 	/** most recently selected type of game: scenario, campaign, random map, etc */
 	ADDPREF(mp_level_type)
+	/** most recently selected mp playing mode/connection type */
+	ADDPREF(mp_connect_type)
 	/** list of the last selected multiplayer modifications */
 	ADDPREF(mp_modifications)
 	/** whether to use a random start time for the scenario */
@@ -448,6 +450,7 @@ struct preferences_list_defines
 		minimap_movement_coding,
 		minimap_terrain_coding,
 		moved_orb_color,
+		mp_connect_type,
 		mp_countdown,
 		mp_countdown_action_bonus,
 		mp_countdown_init_time,