Document all public schema

[SamuelDudley]

Refactor modules to seperate dependencies from schema to enable mavros schema to be enabled / built without needing rospy and mavros to be installed.

[SamuelDudley]

Consider mocking everything out and building the schema under a test runner. https://stackoverflow.com/questions/8658043/how-to-mock-an-import

[SamuelDudley]

These docs look nice and embed graphiql
https://github.com/hasura/sphinx-graphiql
https://github.com/hasura/graphql-engine/tree/master/docs
https://docs.hasura.io/1.0/graphql/manual/index.html