Remove redundant .keep file
Fix test helpers for sections

Before this change, the section helper methods took parameters
but then just ignored them.
Refactor manual JSON schema validation

This introduces a reusable validator and moves JSON schema validation to the model.
Refactor section JSON schema validation
Merge pull request #27 from alphagov/refactor-json-schema-validation-to-activemode-validation

Refactor json schema validation to use ActiveModel validation