Waiting until last CPE entry

[vexyl]

Currently, the server does a bunch of CPE stuff before actually getting all the CPE entries from the client. For example, player's that have CPE enabled will receive ExtAddEntityPlayer packets before CPE negotiation confirms support for that entry.

The server should instead wait to add player to the world until some timer expires after receiving an ExtEntry packet, so that the server can assume the client is done negotiating and can continue adding the player.