Add /jalookup command to find a snitch's group by coordinates

This change adds a new command: /jalookup [x] [y] [z] [world].

If a snitch exists at those coordinates, and the user running the command has access to it, the command returns the name of the group that the snitch is registered to.

The primary purpose for this command is to allow a single snitch monitoring bot to be shared by multiple players without sharing their data. However, it's also useful for regular players to see who has placed a snitch far from them that they've been allowed on.