Fixes to kmeans and gmm

• Allows the setting of k-means' oversampling_factor.
• Changes the naming of GMM map parameters.
• Adds a test for GMMMachine.load().
• Applies a threshold to n in ml_gmm_m_step.
• Computes values as float instead of array in GMMStats.

requested review from @amohammadi

assigned to @ydayer

mentioned in merge request bob.bio.gmm!29 (merged)

merged

mentioned in commit 768d6ba5