Resolve "Refactor Tracker::track()"

Splitted the track method into:

• track
• void trackFeaturePointsLK(int level);
• void refineViaColorPointLK(int level, float errorScale);
• void useBackgroundFilter(QList& trjToDel, BackgroundFilter *bgFilter);
• void refineViaNearDarkPoint();

Also added:

• void preCalculateImagePyramids(int level); Which doubles the performance (10 minutes on the regression test instead of 20)

All in all:

• Split Tracker::track for readability
• Added Doxygen comments
• Precalculate image pyramids
• Factored merging out of Tracker::insertFeaturePoints

Closes #18 (closed)