feature: Provide support for server authentication

Provide capability to specify username and password, and pass those credentials on in the Ajax request. Enable user
to turn credentials on and off.

NB: Server password is stored in memory as cleartext. Credentials should only be used for testing purposes, and not
in a production environment with significant security constraints.
fix: Handle server authentication without popup

The previous implementation of autehnticating to the server was not working properly, and the
browser was opening a popup prompting the user for credentials. The implementaiton was changed
to set BASIC authentication info in an HTTP header instead of settng user and password values
on the XmlHttpRequest.