Refactoring of rpc module
    
    The rpc module is now separated from display layer.
    
    There are two new global topics:
    - 'rpc-start' for showing the widget which indicates execution of rpc calls
    - 'rpc-end' for hiding the widget which indicates execution of rpc calls.
    These two global topics replace the original methods IPA.display_activity_icon() and
    IPA.hide_activity_icon().
    
    There is also new property of a command (notify_globally), which allows to turn off the widget
    which indicates network activity. Instead of classic activity indicator there can be
    called custom function at the beginning and at the end of network activity.
    
    There are also changes in internal communication in rpc.js module. There are four new
    events, two for calling on_success and on_error methods and two for calling custom functions
    at the beginning and at the end of network activity.
    
    https://fedorahosted.org/freeipa/ticket/6144
    
    Reviewed-By: Petr Vobornik <pvoborni@redhat.com>