pwclient: basic python3 support

pwclient: basic python3 support

This fixes a few random issues to make the script work at least somewhat
under python 3:
- set the default encoding to utf-8
- handle xmlrpclib/xmlrpc.client module renames
- handle ConfigParser/configparser module renames
- add a unicode() stub for python 3
- fix old style class definition w/Filter
- use list comprehension instead of map()
- drop the unused version= keyword w/argparse

The code still runs under python 2 the same as before, and now works for
the most part under python 3 -- the handling of encoded content still needs
some work, but that'll require more surgery, and is best left to another
commit after this.

Signed-off-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Stephen Finucane <stephen.finucane@hotmail.com>