[Mac] Added support for global-menu.
-Added MacMenuReceiver class
-Added MENU_RECEIVER as receiver for action's signal
[Mac Global Menu] Added some new slots to support our MENU_RECEIVER idea.
Enabling actions moved to MacMenuReceiver.
[Mac] Create menubar's instance just for FirstAppWindow
[Mac gobalmenu] Fixed issue about bookmark menu and sidebar menu.
[Mac] Fixed, actions were not triggered.
Updated .gitignore and fixed a typo
Merge pull request #749 from srazi/mac_global_menu

Added support for Mac global menu