Added the color white to the notification colors of the LED.

I have added white to the list of possible colors for the notification LED, because I simply missed it.

This is my first code contribution to an open source project ever. Also, this is my first productive usage of git and github. So if there are some rules I don't know about in this context and I have offended someone, please be forgiving and tell me about it.
As if this would not be enough, this is also my very first contact with Android code. I have tested my changes in an emulator, but it unfortunately lacks an emulated LED, so I was only able to test if one can choose white in the settings menu and wheter the translation happens correctly. I would like to have tested it on hardware, but I currently only have one phone that I have to rely on and I cannot risk to break it. So I would be very greatful if someone could do this.