setbgm - new addon

I figured out how the Orchestrion sets the background music in your Mog House and this lets you set it to any music in the game.
Don't need to, was just a suggestion, since I find the opposite more readable. Then you immediately know that the function is called in the `addon command` event, otherwise you see a function and then have to go check where it's used. But that is just my preference, you can keep it this way, just thought maybe you didn't know it worked this way.