This change moves the ConsoleUI class from rb-site out into

reviewboard.cmdline.utils.console. This cleans up rb-site's code and

is a stepping stone toward rethinking some of that interface to benefit

our other command line tools.
No logic has been changed in ConsoleUI. This is a purely mechanical

change.

Ran a full rb-site install, rb-site upgrade, and rb-site --help.

Everything worked as before, and output was as expected.