SRADA-941 Short cut Ctrl-o and Ctrl-s now opens same dialogs as menu items.

SRADA-941 Short cut Ctrl-o and Ctrl-s now opens same dialogs as menu items.

 * In MenuBar added public void showLoadDialog(), that encapsulates all
   trace load call activity.
 * showLoadDialog() calls from ShortCutKeyBindingHandler to avoid another
   implementation of same functionality.
 * showSaveDialog is public now and calls from ShortCutKeyBindingHandler too.
 * In MenuBar added public method isMenuItemEnabled(..).
 * Check for buttons being enabled added to ShortCutKeyBindingHandler to
   make Ctrl-s and Ctrl-o enabled only if Menu button is enabled.
Change-Id: I43b4b82b3fb56dae36e8ae6ec09c276c025fdc79