Fixed SceneInspector inheritance window layout glitch.
Fixed SceneInspector inheritance window layout glitch.

I don't fully understand what is happening but I think it's because when we use the auto-parenting mechanism for a parent which is already visible, Qt realises the child QWidgets earlier in the process, and then fails to update the layout when we change their properties subsequently. By using `_mainColumn()[:] = rows` we not only avoid this, but also do the deletion of existing rows and addition of new ones in one go, which cuts down on intermediate updates and gives a snappier build.

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