ENH MneExperiment cluster report: section headings

Don’t repeat “Clusters in” every time
ENH plot.brain.bin_table():  expose summary method as kwarg
FIX testnd:  standard permutation test (tailedness)

make probability map into LazyProperty
EXA meg:  ADD basic permutation test
EXA meg:  ENH cluster permutation test
FIX MneExperiment._process_subject_arg():  set group value
DOC ClusterDist.masked_parameter_map()
API testnd.anova():  add .effects attribute with effect names
WIP mne API Label.fill()
WIP MneExperiment:  make report for threshold-free permutation tests