Implemented custom param interacts (can be tested with the Prop tester).
Also update openfx.
Revert back the calls of largest enclosed to smallest enclosing as it
was prior to the commit of May the 27th
(also remove the scissor tests in the drawing function of the viewer
which is useless)
Merge branch 'workshop' of https://github.com/MrKepzie/Natron into workshop

Conflicts:
	Engine/Knob.cpp