Merge: Fix model_json and nitweb

Was broken since #2312

* Migrate `model_json` to new serialization API
* Add tests to `model_json` to ensure this doesn't happen anymore
* Migrate `web` package and `nitweb` to new API

@xymus a lot of serialization for you. Note: for each entity, I needed two deserialization version `full` and no full. Wasn't sure on how to handle this concern properly with your API

Pull-Request: #2327
Reviewed-by: Alexis Laferrière <alexis.laf@xymus.net>