Serialization format for defining queries externally

[YakBarber]

Misc notes:

• Answer serialization should be able to reference properties of the Query
• Answers should be reusable in some way
• JSON seems easiest and most widely supported, even if it's ugly. Greater functionality can be added with JSonnet, but probably the better way to handle this is to rely on external tools/scripts to generate the JSON instead. We can use JSON Schemas to define the proper format.