1.$.fn.menubar initial method has the context argv. so Helpbar can pass
itself as context into menubar. in all the callback, 'this' keyword is
reference the bar.
2.menu builder will check click is function or not, if not function, set
the empty function.
1. pass internal using function from $.fn.menubar to HelperBar
1. remove the agent variable for internal using utils. create a method of
menubar ( $.fn.menubar('getInternalUsingUtils')) to get _ functions
object.
2. remove all context parameter inside the menubar functions. use
bar_context private proporty to store the bar context when initialization
of menubar happen. reduce code and better readability.