Add support for multiple queued TPA requests

[JRoy]

This PR adds support for players to receive multiple teleport requests, which are queued and can be managed independently of one another.

All commands should retain their current behavior but have some new additions;

• /tpaccept: now allows you to specify a player or * to accept a specific player's or all players' teleport request(s) respectively.
  • Using a wildcard will only accept all tpahere requests, as players can't teleport to multiple places simultaneously.
• /tpdeny: now allows you to specify a player or * to deny a specific player's or all players' teleport request(s) respectively.

This PR also adds a new setting for the maximum amount of pending TPA requests a user can have at once.

# The maximum amount of simultaneous tpa requests that can be pending for any given user.
# Once at this threshold, any new tpa requests will bump the oldest tpa requests out of queue.
# Defaults to 5.
tpa-max-amount: 5

Closes #3769
Closes #1550

[JRoy]

Concerns Addressed

:DinkDonk:

nitpicking and bias