Extend chat command auth

[Nocturnal42]

Update the auth functions to include differentiation between local mods and global mods. Add singular auth functions like is_owner() is_global_mod() is_local_mod() for cases where differentiation based on a returned int value is not ideal.

Add a "whitelist" auth level. This should be fairly simple, since it will use almost identical code to the mod list, but with a few extra chat commands to add / remove people from the whitelist. Might want to also look at dumping / loading the whitelist from a file to make it persistent.

Related to #16