Support BungeeCord player data on connect

Adds support for BungeeCord player data, in particular player IP, which is otherwise hidden by the proxy, and the player properties, which cannot be retrieved from the auth server because the server has to run in offline mode.
It is not yet possible to get the hostname with which the client connected to the server in Glowstone, therefore the hostname which is also transmitted by the BungeeCord is dropped in the process. The code required to get the hostname is included in this PR, it's just commented to not raise warnings about being unused.
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