Optional inputs are now displayed with a lower opacity than non
optional inputs.
Masks are displayed with dashes.
By default optional inputs (et masks) are hidden if the node is not
selected or hovered by the mouse, to avoid cluttering the UI.
This can be toggled on/off in the preferences (Nodegraph) or in the
right click menu.
Merge branch 'workshop' of github.com:MrKepzie/Natron into workshop