Add: LAN mode with fixed hour (option), user defined nicknames

Just to make multiuser easier to use in my house, I've added a simple "LAN mode".

Also:
- command line arguments, parsing and help messages.
- set the hour and make time move very, very slowly (basically fixed hour).
- set the seed (not sure that works or is useful).
- `/nick` command to pick arbitrary nicknames (LAN mode only).

**Important**: _Do not use LAN mode on the public internet! You will get nothing but grief._