reduce dependency on essentia

[georgid]

Copy the essentia c++ code for extraction of MFCC in repository. This way the dependency on essentia will be not needed.
MFCC extraction is done in FeatureExtractor._extractMFCC

[georgid]

One way is to do a static library out of essentia using .waf and the flag --build-static. In order not to compile the whole essentia, one can include or exclude algorithms using a flag for that. see here.