Allow transparency for point displacement circle/label colors

(cherry-picked from 8f0ed61)

Author: nyalldawson

src/gui/symbology-ng/qgspointdisplacementrendererwidget.cpp

@@ -97,8 +97,10 @@ QgsPointDisplacementRendererWidget::QgsPointDisplacementRendererWidget( QgsVecto
 
   mCircleColorButton->setColorDialogTitle( tr( "Select color" ) );
   mCircleColorButton->setContext( "symbology" );
+  mCircleColorButton->setAllowAlpha( true );
   mLabelColorButton->setContext( "symbology" );
   mLabelColorButton->setColorDialogTitle( tr( "Select color" ) );
+  mLabelColorButton->setAllowAlpha( true );
 
   mCircleWidthSpinBox->setValue( mRenderer->circleWidth() );
   mCircleColorButton->setColor( mRenderer->circleColor() );