Unit tests: create mock KQ cab

[KevinSnyderCodes]

(Local branch: feature-kqcab)

Create KQCab class that mocks a real Killer Queen cabinet:

• Stores connections to the cab
• Sends an appropriate alive message every 5 seconds
• Closes a connection if a response was not received within X amount of time from alive message
• #send(message: string): sends raw message to all connections

Bonus points for verifying the validity of the mock class:

• Does a Killer Queen cabinet accept multiple connections at once?
• What kind of response does a Killer Queen cabinet need to receive after the alive message to keep a connection open?

[KevinSnyderCodes]

Implementation complete! Writing unit tests, then I'll make a PR.