Restyle the pull requests list page
    
    This changes the list of pull requests to match the recently
    re-done issues list.
    
    It only implements the filters and sorting that was in the
    old pull-requests page. (which has fewer options than the
    issues page)
    
    Fixes #3341
    
    Signed-off-by: Ryan Lerch <rlerch@redhat.com>