AppIndicators and GTK Tray Compatability

Hey Mark, I just merged your app indicator code into mine, please test this out and maybe merge??

I think some work still needs to be done in the following areas

1. Where will btsync store its standard config file?
2. Should we break out the gtk tray stuff into a separate .py and have it get imported?
3. I change the class name and some documentation stuff, So just a heads up if you do merge it.
4. Had to remove OS specific package detection, it broke things on my Gentoo system

Right now it tries for appindicator and if that fails uses gtk tray as a fall-back...