Add sound volume management and language selection

Not all translated yet though

default_bus_layout.tres

@@ -0,0 +1,21 @@
+[gd_resource type="AudioBusLayout" format=2]
+
+[resource]
+bus/1/name = "SFX"
+bus/1/solo = false
+bus/1/mute = false
+bus/1/bypass_fx = false
+bus/1/volume_db = 0.0
+bus/1/send = "Master"
+bus/2/name = "Music"
+bus/2/solo = false
+bus/2/mute = false
+bus/2/bypass_fx = false
+bus/2/volume_db = 0.0
+bus/2/send = "Master"
+bus/3/name = "Dialogs"
+bus/3/solo = false
+bus/3/mute = false
+bus/3/bypass_fx = false
+bus/3/volume_db = 0.0
+bus/3/send = "Master"