* adds geom back writing to form field in case of invalid geometry, so the invalid geometry will be shown again
* updates tests
* fixes bug where race condition of celery workers could lead to duplicates in parcels (needs migration)
* improves frontend layout to display more details on district, municipal and parce group
* improves ordering of parcels
* refactors parcel related models
* improves parcel fetching
* extends and simplifies sanitize_db parcel related code
* improves the way parcel-geometry relations are stored on the DB
* instead of a numerical sequence we switched to UUID, so no sequence will run out at anytime (new model: ParcelIntersection)
* instead of dropping all M2M relations between parcel and geometry on each calculation, we keep the ones that still exist, drop the ones that do not exist and add new ones (if new ones exist)
