Add future API

[rafalp]

This PR adds next package to ariadne_graphql_modules containing future API that supports both schema first and code first approaches to development

TODO

• Fix build (rename type to type_ in class fields and function arguments?)
• Feature parity with previous version (Support Mutation type #33 Support Subscription type #30)
• Compat with old API (Backwards compat with previous version #38)
• MyPy plugin (MyPy plugin #40)
• Documentation (Document next API #39)

GraphQL features

• enum
• input
• interface
• scalar
• type
• union
• Subscription