removed prints
corrected get_name
added simulate_h0 method to two-distribution based test statistics, which allows to sample the null hypothesis. This has to be handled in all methods that compute a statistic. Added handling for linear and quadratic time MMD. Changed the bootstrap_null method to use this flag
moved simulate_h0 flag to linear time MMD since in the case where data is stored, permuting it is easy: data is stored in one single feature object