ImageViewUI : Improve color inspector interaction with heavy nodes
ImageViewUI : Improve color inspector interaction with heavy nodes

- Initialise labels in constructor so that we don't show a weird blank UI.
- Show a tiny BusyWidget during computes, to indicate when the inspected values are not up to date yet.

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