Support body in response

[KitsuneRal]

As of f3d4f3b, GTAD can parse object schemas, including those in the response. Next steps are:

• Move the response structure from CallClass to Call in the model (thereby accepting cases when the two calls having the same name might have different response types - but having two calls with the same name is forbidden by the Swagger spec, anyway).
• Remove the code that checks the response for non-triviality and move the whole block that analyzes the result schema after a Call object creation.
• In Printer, use the (now useable) response structure to fill in correct context values
• In libqmatrixclient code, use the context values (the current blocks of code refer to variables that don't exist in Swagger's intermediate JSON).