Revert "Gathering feedback about flat mode icons"

Feedback gathered, thank you for the patience.

This reverts commit 9e9bae54c7c456584e26b3ca61cdadd3da25726c.

Change-Id: If5be24e9f97f172d9e6f170d80b2747cf3e9dc04
Reviewed-by: hjk <hjk@theqtcompany.com>
Reviewed-by: Eike Ziller <eike.ziller@theqtcompany.com>

share/qtcreator/themes/default.creatortheme

@@ -167,7 +167,7 @@ DrawProgressBarSunken=true
 DrawSearchResultWidgetFrame=true
 DrawTargetSelectorBottom=true
 ApplyThemePaletteGlobally=false
-FlatSideBarIcons=true
+FlatSideBarIcons=false
 
 [Gradients]
 DetailsWidgetHeaderGradient\1\color=ffffff