Documentation: Hide empty tutorials page

etc/doxygen/pages/2.Tutorials.dox

 /**
-\addtogroup Tutorials 2. Tutorials
+\cond DOXYGEN_EXCLUDE
+    TODO: Uncomment once tutorials are available
 
-\defgroup RobotAPI-Tutorials RobotAPI Tutorials
-\ingroup RobotAPI Tutorials
+    \addtogroup Tutorials 2. Tutorials
 
-Tutorials related to RobotAPI
+    \defgroup RobotAPI-Tutorials RobotAPI Tutorials
+    \ingroup RobotAPI Tutorials
+
+    Tutorials related to RobotAPI
+\endcond
 */