0.53.0

• Added the concept of a global format for disconnected nodes along with a format plug.
• Added the Constant node for GafferImage.
• Added the Select node for GafferImage.
• Fixed a bug which prevented Assignment nodes from being connected to Shaders outside the Box containing the Assignment.
• Improved formatting in NumericWidgets.
• Added NumericWidget.valueChangedSignal().
• Fixed bug where editing a numeric plug value using cursor up/down didn’t immediately update.
• Added CompoundDataPlug::addMember() and CompoundDataPlug::addOptionalMember() overloads which take a ValuePlug instead of Data to provide the value for the member.