Create API and use it in Alias command

Pawa's codebase has grown organically since the beginning, first starting with a few commands and then adding more. Because of that, there was no good way of testing the commands. There was no layer between the Discord event listener and the core business logic that interfaces with the database.

This change adds something huge, the Pawa class. This is gonna be acting as a headless version of the Pawa Discord bot, that could be used even if there's no Discord.

This will make the testing much simpler and it should make it straightforward to add more functionality.

Prefix and Slash commands are still kind of a mess, but the duplication should be limited.