Implements #141 normals

Calculate and visualise smoothed normals. The smoothing could be improved to dynamically adjust the smoothing level.

.gitlab-ci.yml

@@ -25,7 +25,7 @@ linux:
   script:
     - mkdir build
     - cd build
-    - cmake .. -DWITH_OPTFLOW=TRUE -DBUILD_CALIBRATION=TRUE
+    - cmake .. -DWITH_OPTFLOW=TRUE -DBUILD_CALIBRATION=TRUE -DCMAKE_BUILD_TYPE=Release
     - make
     - ctest --output-on-failure