Update parts of the repo settings to new UI
    
    This updates a few leftover elements that were missed
    when implementing the new UI.
    
    The pages that let you add groups and users to a repo
    are now styled up with fedora-bootstrap, and use the
    same user search UI as adding a user to a ticket.
    
    The buttons to accept changes to Hooks settings are now
    styled up in the same style as all the other buttons.
    
    Fixes #908