Add support for an access control list for certain bot functions

[pfaffle]

Right now the bot just does whatever it is told, regardless of who is asking, as long as the command is valid. I would like to add some access controls for some of the functions (such as join/part, send message, etc.) so that only bot "admins" can tell the bot to use them.

The config file defines an array called "admins" which contains nicks of the people who should have access to more sensitive functions, but none of the plugins currently use that array to check if a user is authorized to perform those functions. This needs to be implemented.