0.16.0

• Added a StandardNodeGadget::acceptsNodule() method which may be reimplemented by derived classes to control exactly which plugs are represented by the gadget. See GafferUITest.StandardNodeGadgetTest.testSubclassing() for an example.
• GafferUI.StringPlugValueWidget now exposes the internal TextWidget with a textWidget() method.
• GafferUI.TextWidget now supports password style text display, settable with the displayMode constructor parameter, or the setDisplayMode() method.
• New StringParameterValueWidget supports [“UI”][“password”] parameter userData.
• The appearance of disabled buttons is now less confusing.