Add an interface for guild admin's bot configuration

[TemporalAgent7]

The bot configuration currently lives in a file (config.json) and it's only read when the bot boots up. Instead, we should allow configuration changes while the bot is running.

Additionally, we need to provide an interface for guild / server admins to change the bot configuration for their specific server. The interface could itself be a set of discord commands, or a separate web ui (with proper authentication) for example.

Some examples of configuration settings that can be set per-server include the bot's prefix (-d is the default), the list of commands enabled (and which channels should disable certain commands), custom text-only commands, fleet id(s) for profile fleet, and so on.