Added DEPRECATED versions of statistic and variance in streaming MMD

DEPRECATED versions are available with

 - statistic type S_UNBIASED_DEPRECATED
 - null variance estimation method NO_PERMUTATION_DEPRECATED
 - null approximation method MMD1_GAUSSIAN_DEPRECATED
I think the covariance in present implementation is being computed wrongly. instead of computing covariance of mmd estimates between samples (p1, p3, q1, q3) and (p2, p4, q3, q4), pi/qi being the samples in current burst, currently its considering samples (p1, p2, q1, q2) and (p3, p4, q3, q4). I'll take a deeper look into this tomorrow.