Do a bunch of cleanup in contrib/
This change does a bunch of cleanup that we've done in review board but

neglected to do here, including:

- Unicode string migration

- Print function migration

- Remove selenium crud

- Make sure all commands run their code from an "if __name__ == '__main__"

  block.

- General import maintenance and cleanup

- Pull in "input" from six.moves

- Make the extension generator create code with the above improvements

Verified common scripts still did their thing
Generated an extension and checked the output