Added flag support to document server.

The document server now supports non-standard port configurations through
the optional flag "-p". Omitting the flag makes the server use the default
port 4343. As a side-effect of making the port configurable, the ports are
now stored as integers and the concatenated network addresses are build with
the functions "addr()" and "heartbeatAddr()".
Changed port to int in load balancer.

To comply with the changes made to the document server to allow ports to be
configurable, the load balancer now also stores its (not-yet-configurable)
port number as an integer and accesses the complete network address through
the function "listenAddr()".
Formatted code to comply to Go formatting standards.