Draft: Exporting stats to csv functionality, multi-view & regenerate stats button

#50 #48 The changes are marked with red:

We calculate stats for the default view (Overview), then all groups/subgroups existing in that edition (Groups), all repositories/subrepos in that edition (Projects), all individuals in that edition (combined stats in that edition e.g. if user A has 1 commit in repo 1 and 1 commit in repo 2, we show that they have 2 commits).