Add functional tests

We should test the functional aspect of aquedux-server and aquedux-client working together to avoid regression in the future as much as possible.

* [ ] Mock redis

It is hard to find a recent/used redis-node mock. Maybe we should consider doing one?

* [ ] Mock sockjs

We could use: https://github.com/thoov/mock-socket

* [ ] Write basic aquedux situation tests