Add a "Specilals" menu for mask mode

W-menu in Movie Clip editor in Mask mode is useless:

But following parodigme blender (same keys do similar things in different places) we must add similar menu for mask-specific actions, like in curve's edit mode in W menu we have actions specific to current mode and context: Such actions like "Switch Direction" i can find only in Tools (T) panel. So lets create new usefull menu for mask mode!