Accept domain names for `multiplayer.connector` config

[Indy2222]

Currently, only IP based socket addresses are accepted for multiplayer.connector. Generalize this so that a domain name is accepted as well. For example connector.de-game.org:8082 should be accepted.

Resolve the domain name while connecting to the lobby server. Use the original address (before resolution) when creating the game in DE Lobby so that other clients resolve it themselves.