Handle empty USB and other things

* Remove mbcuStrings.py - it was a crutch anyway and
	introduced a number of errors
* Handle case where use attempts to download/copy .iso
    to device that has not yet been cleaned or had grub
    installed (i.e., an empty USB device).
* Made the application run as root only. Allowing user
    to run as non-priv was just causing too many head-
    aches. But, updated the start-up script to get the
    user's name and provide that as an argument to the
    main script - now the FileChooserDialog will open,
    by default, in the user's /home.
* Killed the "Refresh" button bug - now, when the
    user clicks on "Refresh" and the currently selected
    USB device is not yet mounted, the user is asked
    to mount the device. All sizes update appropriately
    in this case.