LINUX: check for root, and list devices if device are not given

[sigboe]

The script now checks if you use it as root/sudo, since its required.

If no device is given, it still gives the same error and exits, but it lists usb storage devices and their names for the convenience of the user.

Also:

• Don't require full path to device
• touch up code a bit
• double quote all variables
• The initial splash text in the script is now a multiline variable so its easier to work with in the future.