Add option to only have accelerometer action when screen is on

I like the accelerometer action functionality, but it really doesn't work if you use your phone as a music player when moving around, so I thought I'd add a config option to be able to have it work only when the screen is on. After using it I'd probably prefer it only work when the screen is unlocked but I'm not familiar enough with the ADK to know how to do this so I thought I'd leave it for if this gets accepted.

I hope things are clear. The only definite issue I can think of is with translations, as there are new config options that would need to be translated.

Cheers,
Rich