GafferUI : Add custom node gadget for BoxIO
GafferUI : Add custom node gadget for BoxIO

This uses PlugAdders to allow the user to set up the node with an appropriate plug, and replaces the usual node name label with a label showing the name of the promoted plug.

johnhaddon/gaffer,hradec/gaffer,andrewkaufman/gaffer,appleseedhq/gaffer,andrewkaufman/gaffer,lucienfostier/gaffer,ImageEngine/gaffer,hradec/gaffer,andrewkaufman/gaffer,GafferHQ/gaffer,andrewkaufman/gaffer,ImageEngine/gaffer,ivanimanishi/gaffer,appleseedhq/gaffer,hradec/gaffer,ImageEngine/gaffer,ivanimanishi/gaffer,boberfly/gaffer,lucienfostier/gaffer,boberfly/gaffer,ImageEngine/gaffer,appleseedhq/gaffer,GafferHQ/gaffer,lucienfostier/gaffer,GafferHQ/gaffer,hradec/gaffer,ivanimanishi/gaffer,hradec/gaffer,johnhaddon/gaffer,andrewkaufman/gaffer,johnhaddon/gaffer,ivanimanishi/gaffer,boberfly/gaffer,johnhaddon/gaffer,johnhaddon/gaffer,GafferHQ/gaffer,appleseedhq/gaffer,GafferHQ/gaffer,lucienfostier/gaffer,boberfly/gaffer