Fix ability to test json payload against json schema

Conflicts:
	src/Context/JsonContext.php
Merge pull request #2 from gmorel/fix/allow_schema_deep_validation_stephpy

Fix/allow schema deep validation stephpy
Content given to the resolver has to be an object (deserialization of a json content).
Fix step  `the JSON node "Item[10]" should not exist` when node is an array