FeatureExtract/FeatureExtract.cpp
* Added commented pieces of code coming from the initial test of using
detect/extract features in OpenCV since they might be useful later for
debugging or performance measure purposes.

VocabLearn/VocabLearn.cpp
* Deleted commented code containing code from the first implementation
of the full retrieval process.

VocabLib/tests/Makefile
* Changed gtest for the latest locally compiled version.

VocabLib/tests/VocabTree_test.cpp
* Implemented test for methods related with the filling and usage of
inverted files.