Make launchpadlib support positional parameters when invoking named operations

[Leonard Richardson]

To invoke a named operation from launchpadlib you must use keyword parameters, unless the operation only takes one parameter. Supporting positional parameters in general is a bit of work but it can be done.

1. Change the operation_parameters declaration method so it takes a list of fields, not a set of kwargs.

2. When exporting WADL, give the parameters of a named operation in the order they were exported, except put optional fields at the end.

3. Change launchpadlib to support *args, matching them against the WADL parameters in the order they were exported.