Tweaks to the title screen, mainly for 800x600

Also:
- Hide cores button if there are no addon cores installed
- Remove "failsafe" core since it didn't work as advertised

data/cores.cfg

@@ -15,12 +15,3 @@ One Multiplayer Campaign with 14 Scenarios,
 500+ Add-ons.)"
     path="/"
 [/core]
-
-[core]
-    id=default_
-    name= _ "Wesnoth (Failsafe)"
-    rank=10
-    image=icons/icon-game.png
-    description= _ "Loads only mainline Wesnoth data without any add-ons."
-    path="/"
-[/core]

data/gui/widget/button_default.cfg

@@ -211,6 +211,7 @@
 	id = "large"
 	description = "Large button"
 
+	{_GUI_RESOLUTION (window_width, window_height = 850, 650) 40 112 26 13 4 ({_GUI_BUTTON_FONT_SIZE}) () 255}
 	{_GUI_RESOLUTION () 40 116 30 13 4 ({_GUI_BUTTON_FONT_SIZE}) () 255}
 
 [/button_definition]

data/gui/widget/panel_title_screen.cfg

@@ -75,6 +75,7 @@
 	id = "title_screen"
 	description = "Definition of the panel for the title screen"
 
+	{_GUI_RESOLUTION (window_width,window_height = 850, 650) 10 5 10 5}
 	{_GUI_RESOLUTION () 25 5 9 14 }
 
 [/panel_definition]

src/gui/dialogs/title_screen.cpp

@@ -17,6 +17,7 @@
 #include "gui/dialogs/title_screen.hpp"
 
 #include "game_config.hpp"
+#include "game_config_manager.hpp"
 #include "game_preferences.hpp"
 #include "gettext.hpp"
 #include "log.hpp"
@@ -356,6 +357,11 @@ void ttitle_screen::pre_show(twindow& window)
 			std::bind(&ttitle_screen::show_debug_clock_window,
 						this,
 						std::ref(window.video())));
+
+	auto cores = game_config_manager::get()->game_config().child_range("core");
+	if(cores.size() <= 1) {
+		find_widget<tbutton>(&window, "cores", false).set_visible(twindow::tvisible::invisible);
+	}
 }
 
 void ttitle_screen::update_tip(twindow& window, const bool previous)

src/wesnoth.cpp

@@ -831,7 +831,7 @@ static int do_gameloop(const std::vector<std::string>& args)
 
 			int current = 0;
 			std::vector<config> cores;
-			for (const config& core : game_config_manager::get()->game_config().child_range("core")) {
+			for (const config& core : config_manager.game_config().child_range("core")) {
 				cores.push_back(core);
 				if (core["id"] == preferences::core_id())
 					current = cores.size() -1;