feat: app assembly

[jasonkuhrt]

Motivations:

• decouple concept of starting server from assembly to support future serverless feature Serverless mode #782
• assembly is the process of gathering the lazy state into a final runnable one
• settings is now a component like schema and server
• the components are designed to look a lot more symmetrical now
• root app state is passed down to components which attach their namespaced state to, easier to reason about, think redux
• introduce concept of checks that runs after schema assembly

BREAKING CHANGE:

• server.start and server.stop are no longer exposed. If you had a use-case for them please open an issue to discuss.

TODO

• docs
• tests