Implement authentication over TCP connection.

[bbuck]

Connections should be handled by a state-storing client object and have to authenticate with a player record.

A good set of exit criteria:

• (code) Represent connections as clients one fired off that stores state for the connection.
• (interaction) User must authenticate by entering player name and password when prompted
• (interaction) Once authenticated user is (for the time being) dropped into a global chat space.

[bbuck]

This will be done in a plugin, I'm going to call BasicPlayers or something similar. It will feature a Player entity with a username and a password and authentication and association to a client. But that work will get done in the plugin so this issue is no longer valid for this repo.