Support for callbackURLs in the Google, Yahoo and OpenID logins

http://jira.webinos.org/browse/DEVPORTAL-9

This is a simple fix that allows the config file to have alternative callback URLs for the
authentication providers.  This is helpful when working on a system where the internal URL of the server is, say, https://x.x.x.x:6443/ but the external is https://x.x.x.x/.  Without this, we can't do port forwarding.

The changes just involve adding a variable to the configuration file and modifying the auth.js and passportconfig.js files to load and read them respectively.

This is part of the effort to make the PZH web server run as a non-super-user.

Jira issue: DEVPORTAL-9