change to working dir for the scripts that use util/.

This may help in refurbishing an x230 laptop.

the update function already uses it

All we do is the bios vendor/version check. We can do that in any case.
Requirements don't change.

Fixes #56
Closes #58

also, we use the check for x230 in the flashing scripts now. They have
to be run as root now.

Now our scripts start with _where_ it should be run. x230_*.sh should
be run on the x230 where Skulls should be installed. external_*.sh
obviously not.

This also adds the -f <flasher> option and an interactive menu if not
specified.

work in progress #18