Base: Move App::Color to Base

Every basic data type is stored in Base module, color is standing out as
one that does not. Moving it to Base opens possibilities to integrate it
better with the rest of FreeCAD.

src/Mod/TechDraw/Gui/TaskSelectLineAttributes.h

@@ -85,7 +85,7 @@ class Ui_TaskSelectLineAttributes;
 //     float getWidthValue();
 //     void setColor(int);
 //     int getColor() const {return color;}
-//     App::Color getColorValue();
+//     Base::Color getColorValue();
 
 // }; // class lineAttributes