Improve validation error messages

[roll]

Overview

For now validation error messages are mostly useless. It's because we use JSON Schema validation and get a lot of messages like this:

• Descriptor validation error: Data does not match any schemas from "anyOf" at "/resources/1/schema/fields/0" in descriptor and at "/properties/resources/items/properties/schema/properties/fields/items/anyOf" in profile

This topic has been already touched by @Stephen-Gates and his team. So it's kind in the air. Other question what changes we should make in datapackage-js or in profiles to improve the situation.