Split Web UI initialization to several smaller calls
    
    https://fedorahosted.org/freeipa/ticket/1933
    
    Web UI init method was modified to get initialization data in 3 calls.
    First call remains the same as before except that the json_metadata command
    was removed.
    
    JSON metadata are requested after successful response of the first batch command.
    This approach should preserve functionality in IE (where request is missing after
    authentication). Getting JSON metadata is split to two commands - this should prevent
    the error in linked ticket. These two commands are paralelly executed by new
    concurent_command object.
    
    Concurrent command waits for all responses then it calls each command's success
    handler.