Background re-authentication

Added logic to attempt authentication in the background before displaying the embedded browser, which allows a seamless re-auth (after initial login) if the user chose to have their credentials cached by the browser during  initial auth.

If seamless re-auth is unable to be performed (eg no cached credentials, or initial auth scenario), the browser is then displayed pointing to the last page which was reached in the OAuth cycle - which should be either the widget page or the specified provider login screen.