Validate that schema's fields match __init__ args of related model for Resources with "POST" method.

[dmitrymishanov]

The purpose of this validation is to "fail early" if developer has made a mistake with fields.
I reverted commit with an attempt to implement such validation, because it didn't consider that validation is needed only for "POST" method (because schema fields will be used as args for model.__init__) and that some fields like serial primary keys should be generated automatically.