MFSideMenuStateEventMenuWillOpen: Distinguish between left and right menu

[ankraft]

Would it be possible to add to the notification which menu (the left or the right one) will open? This would help in the reduction of possible updates in case an application makes heavy use of menus in multiple view. Perhaps adding two new notifications such as MFSideMenuStateEventLeftMenuWillOpen and MFSideMenuStateEventRightMenuWillOpen would help.