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
Each of those enums should be documented. At least providing a link towards where the information about them is in doxygen. So that users can easily click through this stuff