Masterserver

automatic announce to masterserver on start and every 300s
more info about servers, number of clients, flags (creative, damage, password, .....)
data exchange via curl + json
new jsoncpp lib from http://jsoncpp.sourceforge.net/
masterserver script included in utils/
already ran at http://servers.minetest.net/
new conf vars:
```
# Name of server                                                                                                                                      
#server_name = Minetest server                                                                                                                        
# Description of server                                                                                                                               
#server_description = mine here                                                                                                                       
# Domain name of server                                                                                                                               
#server_address = game.minetest.net                                                                                                                   
# Homepage of server                                                                                                                                  
#server_url = http://minetest.net                                                                                                                     
# Automaticaly report to masterserver                                                                                                                 
#server_announce = 0                                                                                                                                  
```