Multiplayer: Masterserver debugging/extension

[smerkli]

For a multiplayer game to be playable online, a central "master server" is required that the game clients connect to. The task of this master server is to keep a list of all multiplayer game servers and their IPs so players can select which server to connect to.

The current state of the master server is a basic implementation with some memory leaks still present. More debugging work is required to make it useful as well as some extensions for easier management.