[improvement] store the credentials user input as a ViewController field and skip the dialog

[dodikk]

A heads-up to the future library users.

In my case the web page contains a video playback link.
Both the page and the video are hosted as corporate resources and require the ADFS authorization.
When the video playback starts, the user is overwhelmed with the "please enter credentials" alerts.

P.S. That's pretty easy to fix. No library modification is required. It affects only the demo project code. I'll send a pull request addressing this issue soon.

[dodikk]

Added memoization in #7

[hborders]

This is a fine refactor. Making the example more fully functional is great!