Schemas 1.0 + serializers tests

- Upgrades marshmallow version => 1.0.0a and migrates code to use marshmallow's new serialization API
- Rename `Serializers` => `Schemas`
- Expands test coverage of the `neurotrends.api.serializers` module
Does `scratch_articles` need to be injected here, since it's already been attached to the class?