Support additionalProperties

This is a large change which refactors a lot of code to add
additionalProperties support. For each structure which has
additional properties, we make sure to generate a Go type which
implements the JSON marshal/unmarshal interfaces.

Author: mromaszewicz

oapi_validate_test.go

@@ -131,7 +131,7 @@ func TestOapiRequestValidator(t *testing.T) {
 				return errors.New("forbidden")
 			},
 		},
-		UserData:"hi!",
+		UserData: "hi!",
 	}
 
 	// Install our OpenApi based request validator