Run Plinth setup during FreedomBox setup

Created by: SunilMohanAdapa

Start DBus daemon to ensure PackageKit can use it. Only start if it is not already running. Stop after setup. Stop only if we have started it.

I have done some manual unit testing on the patch. However, i have not tested with either full image or installing through Debian package. Not sure if I will get the time to do it in next few days. I could use some help doing this.