Added a server info http page

The server info is in JSON and sorted alphabetically.

Also added the maxPlayers setting and it is working; added the
serverName setting for the upcoming server list.

Credits to KMP and their contributors for the JSON server status page (actually I thought of it before checking KMP's GitHub :D).

Example JSON:

```json
{"cheats":true,"game_mode":"SANDBOX","max_players":0,"mod_control":true,"player_count":0,"port":6702,"server_name":"DMP Server","warp_mode":"SUBSPACE"}
```