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
@karlnapf @sejdino added covariance computation without permuting as well. here we don't use DEPRECATED blockwise statistic computation though. Just for covariance the samples are not randomly shuffled when null variance estimation method is NO_PERMUTATION_DEPRECATED.