Added bg_sound manager and according ESC command.

Started transitions scene.

game/ui/commons/pause_menu/pause_menu.gd

@@ -0,0 +1,17 @@
+extends Control
+
+
+func _on_continue_pressed():
+	escoria.main.current_scene.game.pause_game()
+
+
+func _on_save_game_pressed():
+	pass
+
+
+func _on_load_game_pressed():
+	pass
+
+
+func _on_quit_pressed():
+	get_tree().quit()