Add error message for code generation

- Useful to show valid targets
commit generated models and json in API

- just using for Code and CodeError. need to refactor some of the existing
  code, before it can use generated models.

- generate code that uses scala.collection.Seq instead of
  scala.collection.immutable.Seq. The one in immutable is
  a subclass of Seq
fix test
add support for separate specification of query params
add support for body
add body and full query support to scala
add query and body support to ruby

- added an == override to make testing easier
- make reference API a bit more idomatic
fix play routes test by adding a user_form and bodies
cleanup Members controller in reference api
remove concept of form params
update api.json with bodies on all POSTs

- for now parameters is a synonym for query...
add unit and file body types
remove unused isDefault attribute from Body
remove query attribute

Since the parameters attribute can still include
path params, it makes sense to put the query params
there too.
validate body types
add helper class in companions for PATCH
isJsonDocumentMethod => bodyAllowed
add patch classes in the other scala targets

- add json reads/writes
- add scalacheck generators
- add to reference API
add TODOs