1) A /v2/keys controller.
2) Separate wire protocol PreKey POJOs from database PreKey
objects.
3) Separate wire protocol PreKey submission and response POJOs.
4) Introduce a new update/response JSON format for /v2/keys.
1) Store account data as a json type, which includes all
devices in a single object.
2) Simplify message delivery logic.
3) Make federated calls a pass through to standard controllers.
4) Simplify key retrieval logic.
