Run a spell-check over all project files
docs: Fix spelling errors & do minor improvements
Restore terminal attributes on exit

If a dialog widget exits in an abnormal way, we may end up having a
messed up terminal. Make sure that the terminal attributes are always
restored before the dialog-based version on snf-image-creator
terminates.
Remove warning about snf-image-creator name change

Remove the warning about having swapped the names of the snf-mkimage and
snf-image-creator executables. Keeping this warning for one major release
was enough.
Save traceback for unhandled exceptions in a file

If an exception that we don't know how to handles gets thrown, print a
message about the existence of an unexpected error and save the
traceback in a temporary file before exiting.
Handle guestfs.launch() thrown RuntimeErrors

If launching the guestfs helper VM fails, the library will throw a
RuntimeError exception. Don't treat this as an unhandled exception.
Convert it to FatalError but preserve the error message.