added a CachingFeatureExtractor that stores extracted patches for later additional retrieval
* renamed PyramidFeatureExtractor to DirectPyramidFeatureExtractor
* added a new interface named PyramidFeatureExtractor
* added new pyramid-based feature extractors for additional filtering (FilteringPyramidFeatureExtractor) and caching patches (CachingPyramidFeatureExtractor)
added possibility to let DirectPyramidFeatureExtractor build the pyramid, no explicit pyramid building necessary anymore
replaced old timing calls of tracking apps by the new c++ chrono lib
Merge branch 'refact' of github.com:elador/FeatureDetection into refact
* added missing include of stdexcept
* changed PyramidFeatureExtractor to DirectPyramidFeatureExtractor