Performance Issues

- [x] https://github.com/tnc-ba/strongTNC/commit/6ae842593105e8a5e1396ff93fc5bd46bab6f9c3#commitcomment-6547634
- [ ] SWID Inventory (E-mail Tobias)
- [ ] Inventory View Performance
- [ ] Log View Performance
- [x] TagStats Model
- [ ] Rename / Move methods (e.g ``get_installed_tags_with_time``, ``get_installed_tags_dict``)
@d22 Does the __``isnull`` and ``distinct`` make sense here? As far as I can see there is no tag field and sessions are always distinct? And they are already sorted by ``-time`` in ``the get_sessions_in_range``