Refactor UID/GID generation
In contrast to the old approach, this works on MariaDB and never reuses UIDs/GIDs of deleted users/groups. With the old approach, creating a group with GROUP_MAX_GID broke GID auto-allocation for new groups. The new approach always uses the first unused ID in range. It is also more robust to config changes.
Fixes #160 (closed)
Edited by Julian