* add admin purge user function
* improve comments
* minor naming changes
* ensuer user is enabled for tasks api requests
* add preview with stats to /admin/purge_user/{id} endpoint
* add update_children_counts()
* added root tokens and endpoint for adding api keys
* Change down revision to current alembic head
* removed added_by_root_token
* refactored description
* fixed jinja errors
Co-authored-by: Andreas Köpf <andreas.koepf@provisio.com>