Protocol Layer Refactor

[tli2]

Protocol handler and traffic cop, as it stands currently, are completely intertwined, and rank very high on my "worst code ever seen" list. There is so much duct tape and coat hangers here, it pretty wrecks testability and extensibility of the code. We will have to refactor this in phases.

This PR will separate out all the components like they should be. @ChTimTsubasa is working on another PR based on this to fix the broken transaction handling logic.

[tli2]

There are still failures, I will fix this concurrently with review.

[coveralls]

Coverage decreased (-0.3%) to 76.24% when pulling 2dca58d8964b318d9b9029096ad9b6a545feeaf4 on tli2:tianyu-protocol-refactor-structure into cd681eb256b79001b32f754b235f66c4b189b5ba on cmu-db:master.