#893: configure server address

@dhanya : Code review is done, it looks good! There is one bug though. 

The configured server address should be used by the serverDomain inside PacoClient. Specifically, when user configures the server address, we should change the serverDomain too, so that all the http requests can be sent to the server address the user has configured.

And btw, I've also made some comments about some minor issues too.