DBN insertion into the HTK HMM (viterbi) now working

I did that separately into a batch_viterbi.py because I'm anyway
going to use the GPU to compute likelihoods on the whole dataset
beforehand (otherwise it's much longer).

TODO:
 * adapt the scale of DBN's likelihood to GMM's likelihood
 * acoustic/state-transitions scaling factors
 * bigram models
 * triphones recipees for GMMs
merging / fixing conflicts