Add code to parse configuration options to specify the gecos and username for each server and globally.

With this patch you can specify the gecos (real name) and username for each server separately, and globally, in the configuration file.
A config.js file fragment that uses this functionality is as follows:

--------
conf.default_gecos = 'KiwiIRC';
conf.default_username = 'user';

conf.servers.push({
    port:   9100,
    address: "0.0.0.0",
    default_username: "myusername"
});

conf.servers.push({
    port:     9101,
    address: "0.0.0.0",
    default_gecos: "My real name",
    default_username: "anothername"
});
--------

If a default gecos or username is provided in the servers block, it will be used. If not, the global one will be used. If not provided in any place, the nick will be used as username and a default gecos will be used (as before).