* Port GMock feature from NativeInstruments
swagger-codegen fork:
https://github.com/NativeInstruments/swagger-codegen/pull/9
* Update petstore for Mockable APIs
* Fix shared_ptr in templates for File params
* Add guards in templates for GMock APIs
* Regenerate samples without GMocks
* Add useful constructors for GMock APIs
* Add constructors to API header interface
* Update samples with explicit monadic constructors
* Add default implementations for destructors