Add map downloads

[Fohlen]

We want the players to be able to download new maps. This should work as following:

• there is a setting in the "game" tab whether or not maps will be downloaded
• the player joins a server. If the server uses a unknown map and is not in edit mode, send the map to the player

Technically this can be solved as follows:

• the client has a downloadmaps variable
• the servers has a servercontent variable
  • the server configures a web server on the servercontent address with a packages directory
• when downloadmaps is enabled the client will read packages/base/map.cfg from the address specified (servercontent)
  • the client will download the map, the configs, textures, sounds (...) from the server
  • the client will generate a temporary ZIP archive containing all the content from the server (to avoid collision)
  • the client uses addzip to add the generated ZIP and loads the map regularly

[Fohlen]

This has been solved by #8 Closing for now