Add `dict_to_obj` utility function
Introduce the brand-new SerializerDeserializer API
Fix `DoesNotExist` exception on `dict_to_obj`
Add serialize_message method to {ser,deser}ializer
Refactor REST code based on PEP8
Change RestResource with new ser/des API

Note: responses with nested objects are not allowed anymore. This simplifies
things by now and can be included later (possibly only if `expand=true` is
present on query string).
Refactor admin code using PEP8 rules
Add .gitignore
Add custom ser/des to RestAPI (and tests, of course)