This centralizes the custom help formatter and --version handling from

rb-site into a new reviewboard.cmdline.utils.argparsing module,

allowing reuse by other programs.
The help formatter provides terminal-bound wrapping while also

preserving paragraphs, unlike the default formatter which can do only

one or the other.
The --version action lists the version for the program + Review Board,

the Python version, and the install path for Review Board.

Ran rb-site --version and rb-site --help. Saw the correct output.