Implement catalog plan subcommand

[carolynvs]

FYI, this will follow the new command format from #25 since it's brand spankin' new.

$ svc-cat get plans
# output should include Name, Class, Description and UUID

$ svc-cat get plan <name>
# output will match the list above but will only have a single result in the table

$ svc-cat describe plan <name>
# output will match new `describe` format
# output will include child bindings

[carolynvs]

Fixed by #29