Add validation rules to check for deprecated fields

[stubailo]

The same way this package includes a validation rule to check for unknown fields, it might be valuable to be able to check for deprecated fields as well.

[0xR]

Shouldn't bee hard according to @leebyron:
https://twitter.com/leeb/status/725429815625408512

[helfer]

@0xR if you do it, make sure it's not part of specified rules, because those will make the query fail by default. It should be an optional rule that people can import.

[stubailo]

Should be really easy to copy this rule and modify it a bit: https://github.com/graphql/graphql-js/blob/master/src/validation/rules/FieldsOnCorrectType.js