pwclient: support 'archived' filtering and updating

pwclient: support 'archived' filtering and updating

Examples:

  # Mark patch as uperseded and archived
  pwclient update -s Superseded -a yes <ID>

  # List all archived patches
  pwclient list -a yes

Notably, we still leave the '-s' option as required for 'pwclient
update'; so you can't *just* archive a patch without setting its state.
I couldn't quite figure out the right argparse usage to represent that
the user must include one or both of '-s' and '-a'.

And of course, the server must have an updated xmlrpc that supports the
'archived' field for list filtering (recently patched), otherwise you'll
just get an empty list.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Jeremy Kerr <jk@ozlabs.org>