Addresses comments from https://github.com/LOOHP/Limbo/pull/57#issuecomment-1304543589
In particular:
* Functionality now matches other server types
* only enforce the allowlist if a new "enforce-allowlist"
boolean in server.properties is set to true
* Loads and process the allowlist only once when the server starts (or
the reload command is executed), instead of every time a user connects.
* Add a new command & associated permissions "allowlist reload"
to reload the allowlist
- Added option for Modern Forwarding and BungeeGuard (for proxies that are connected to older servers)
- Made Modern, Bungeecord and Bungeeguard mutually exclusive
- Fixed PacketLoginInPluginMessaging, structure was incorrect
- Added `readUUID` in DataTypeIO