Config server with settings

Added setting interface (ServerSettings and ServerInternalSettings) for server to access its configuration properties.

Enabled to obtain a server property with Config.get + property settings. Replaced the previous Apache Configuration + constant string property-accessing-pattern. 
Same here, lets have Setting<> be the thing you get out here. I'd also suggest we rename this:

    public Iterator<Setting<?>> keys();

I haven't gone far enough down the PR to tell exactly what the use case for this method is - if its used for cloning the Config instance, I'd rather suggest we add a constructor like:

    public Config( Config base ) {}

that creates a duplicate config instance.