Clean up the JSON schema

[samuel-skean]

1. availability should really be a property on members. That makes it so much easier to validate certain things.
2. Maps should probably be represented as lists of tuples. One major benefit might be the ability to use sqlite functions to manipulate the JSON in the database instead of pulling in whole meetings and processing them in javascript, but I haven't investigated that. Regardless, the only thing it's bad for is API prettiness (very subjective), and otherwise it just fights the language and people's expectations less. These aren't records/objects, they are maps. Keys in objects should ideally be reserved for static data.