Added bg_sound manager and according ESC command.

Started transitions scene.

game/ui/commons/main_menu/main_menu.gd

@@ -0,0 +1,20 @@
+extends Control
+
+
+func _ready():
+	escoria.esc_level_runner.set_sound_state(["bg_music", 
+		"res://game/sfx/Game-Menu_Looping.mp3", true])
+
+func _on_new_game_pressed():
+	escoria.new_game()
+
+func _on_load_game_pressed():
+	#  Show Loading screen
+	pass
+
+func _on_quit_pressed():
+	get_tree().quit()
+
+
+func _on_continue_pressed():
+	pass # Replace with function body.