Gui: SoFrameLabel text color from base color support

This adds support for obtaining text color from the state of the graph
(base color) to SoFrameLabel nodes.

src/Gui/SoTextLabel.h

@@ -120,6 +120,7 @@ public:
     SoSFBool   frame;
     SoSFBool   border;
     SoSFBool   backgroundUseBaseColor;
+    SoSFBool   textUseBaseColor;
   //SoSFImage  image;
     QPixmap    iconPixmap;