Improved usability of login dialog
    
    Usability was imporved in Unauthorized/Login dialog.
    
    When the dialog is opened a link which switches to login form is focus so user can do following:
    
    1) press enter (login form is displayed and username field is focused )
    2) type username
    3) press tab
    4) type password
    5) press enter
    
    this sequence will execute login request.
    
    When filling form user can also press 'escape' to go back to previous form state. It's the same as if he would click on the 'back' button.
    
    https://fedorahosted.org/freeipa/ticket/2450