Add tests for Page classes
    
    Adds a whole set of tests for the Page classes. Some slight
    adjustments needed in test_event to have them share fixtures.
    One small code change (using an OrderedDict not a dict) is
    needed for the DownloadPage test result to be consistent on
    older Pythons (before stock dicts started acting like ordered
    ones).
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>