QmlDesigner: use a central notTooBrightHighlightColor()

Change-Id: I71988cda0f9488a59722b00e0c0c0e926a15e7f2
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@digia.com>
QmlDesigner: remove debug enum

Change-Id: Icbb1ac041387b1dda136957c4689b79a5615ed89
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@digia.com>