Extend the 'buildTypeWeights' function to account for SUBSCRIPTIONS in a schema object - including tests

[evanmcneely]

Once this issue gets picked up, our buildTypeWeightsFromSchemaObject should be creating the type weight object out of a schema with query and basic types AND PASSING THE TESTS. Extend this functionality to work for subscriptions.

• Write tests for this additional functionality
• Add functionality to the algorithm to pass the tests.