Fixed color-selection widgets on PropertiesPanel.

Fixed color-seleciton widgets on PropertiesPanel to allow picking "standard
colors". Also fix rendering logic in pqColorChooserButton to work correctly when
the button is resized.

Change-Id: Ia9ac690d515bfd47e1c3d188647347a066680219
Merge topic 'refactor_panels' into next

40a7024 Fixed color-selection widgets on PropertiesPanel.