Moved tutorial table-of-contents files to corresponding root level

doc/tutorials/gpu/table_of_content_gpu.markdown

@@ -0,0 +1,15 @@
+GPU-Accelerated Computer Vision (cuda module) {#tutorial_table_of_content_gpu}
+=============================================
+
+Squeeze out every little computation power from your system by using the power of your video card to
+run the OpenCV algorithms.
+
+-   @subpage tutorial_gpu_basics_similarity
+
+    *Compatibility:* \> OpenCV 2.0
+
+    *Author:* Bernát Gábor
+
+    This will give a good grasp on how to approach coding on the GPU module, once you already know
+    how to handle the other modules. As a test case it will port the similarity methods from the
+    tutorial @ref tutorial_video_input_psnr_ssim to the GPU.