Add Extension Framework with Minecraft Player Manager

[bimbab189]

Review note
Please review only the final commit - the earlier commits were iterative debugging and contain incomplete/buggy code that was fixed in subsequent commits.
Summary
This PR introduces a modular Extension Framework for Jexactyl, allowing server owners to easily enable, configure, and manage extensions on a per-server basis. As a proof of concept, a fully-featured Minecraft Player Manager extension is included. I am also working on making more extensions.
extensions.php
Has documentation on how to add extensions as configurable stuff in the extensions module.
This is a a half complete idea because for a full extension module i would want to have standardized extension frontend components. And some easy way to add them where you could just drop in a few files but it works and allows for easier future development. I can work on improving it if you agree, but right now ill work on more extensions.

[bimbab189]

added attribute manager, player inventory viewer and some other color based changes to match the theme fully

[bimbab189]

still not very happy about it, making some minor fixes/changes

[macery12]

love this idea, ill check it out and review eventually as its a large PR
but feel free to join the discord and discuss more
https://discord.gg/fVJZtqKYrc

[bimbab189]

its finished, please review :)

[bimbab189]

And you are about to do alot more reviewing Xd i have alot of ideas i want to implement mainly in extensions which is why i made that.