Add support for "body" element to explicitly specify type of form body in an operation

Introduce 'body' on operations. For operations that support posting data, you can now specify a 'body' for the JSON document instead of explicit parameters. The body parameter takes a single attribute - type - specifying the name of a model.

Bodies and query parameters are now fully supported in the play 2.3 client and the ruby client.

Query parameter support for operations. When specifying a body, you can also specify additional query parameters for an operation. The parameters section of operations is now interpreted as being in the body by default, and if a 'body' element is provided, the parameters are expected to be sent as query parameters.