Refactor world data to include a registered player

In lieu of full authentication, pre-register a known user (Discord handle) to a world. Check that world's registered user against a bot interaction's user (presuming this info is available on the received interaction).

A world may have more than one registered user (e.g. Factorio, Minecraft, server-based games), i.e. the world name may not directly correspond to a single player / user.