Add deep properties getter utility function to config.

cfg._("a.deep.property") returns the value of
cfg.a.deep.property if it exists. If the property
or any of its parents do not exist, returns undefined.

lib/www/server/lib/config.js

@@ -69,4 +69,6 @@ if (process.env.PGDATABASE) {
 	delete config.db;
 }
 
+config._ = (k) => k.split(".").reduce((a, b) => typeof a != "undefined" ? a[b] : a, config);
+
 module.exports = Object.freeze(config);