Allows builders to dynamically chance the skybox of a box, and play
a different music track.
Works like an extender UI wise. left/right clicking changes the
selected music track or skybox.
When triggered, plays the track selected or sets the skybox.
When untriggered, stops the music or reverts the skybox to the box
default.
This is slightly modified from the skybox mod and puts the clouds
slightly higher to avoid hitting most box sizes.
Skybox command is also back, but it needs the skybox priv.
