Updated: Use singular they for gender equality

I suppose this is more PC, but both versions are grammatically correct.
Updated: Refactored some things
Updated: Remake teleport request system

— UNTESTED! —

This makes all teleport request acceptance commands take a name. One can deny a request from a certain player or accept from a certain player. Multiple requests cannot be made from the same requester to the same target (of any type, i.e. /tpa and /tpahere). All requests expire on restart. Requests cannot yet be viewed, but this is a major step up from the overriding system before. The code is also much cleaner.

TL;DR: Read the first sentence.