Generate GraphQL Type definition without Resolver Map to allow incremental adoption?

[KeithGillette]

In my testing, the buildSchema and buildTypeDefsAndResolvers functions require the resolvers array to not be empty. I'm curious if there's a way to only specify orphanedTypes to allow the GraphQL Type definitions to be built by type-graphql but the Resolvers map to be specified separately, which would allow us to incrementally migrate an existing TypeScript + GraphQL project to type-graphql without having to refactor the entire project at once.

[MichalLytek]

See #339