AnimationGadget : add tie mode options to gadget context menu
AnimationGadget : add tie mode options to gadget context menu

* tie mode can be set in gadget for all selected keys via option in
  right click context menu.

ref #4306

johnhaddon/gaffer,GafferHQ/gaffer,andrewkaufman/gaffer,hradec/gaffer,ImageEngine/gaffer,GafferHQ/gaffer,hradec/gaffer,andrewkaufman/gaffer,johnhaddon/gaffer,hradec/gaffer,andrewkaufman/gaffer,GafferHQ/gaffer,hradec/gaffer,johnhaddon/gaffer,andrewkaufman/gaffer,GafferHQ/gaffer,ImageEngine/gaffer,johnhaddon/gaffer,ImageEngine/gaffer,GafferHQ/gaffer,johnhaddon/gaffer,andrewkaufman/gaffer,hradec/gaffer,ImageEngine/gaffer