Throw error on non-scalar type usage without resolution methods

[mjfwebb]

It would be nice to throw an error on startup when type usage is without resolution methods.

For example, the following would be invalid and throw an error:

type Banana {
  colour: String
}

type FruitBowl {
  banana: Banana
}

This is invalid because there is no resolution method for Banana in Fruitbowl.

Valid resolution methods would be, for example: relationship, custom resolvers, cypher