#50 Overlaying geometries

* refactors geometry field into GeoReferencedMixin, holding more handy methods and used in all models, formerly holding the geometry field
* refactors backend admin configuration, so modified, deleted and created are not editable in the backend which also skips loading of all possible choices
* fixes typo in sanitize_db command
* introduces GeometryConflict model, holding a link between two geometries, where one overlaps the other
* adds first (WIP) messages into detail views of ema and intervention for test purposes

konova/management/commands/sanitize_db.py

@@ -208,7 +208,7 @@ class Command(BaseKonovaCommand):
         if num_entries > 0:
             self._write_error(f"Found {num_entries} geometries not attached to anything. Delete now...")
             unattached_geometries.delete()
-            self._write_success("Deadlines deleted.")
+            self._write_success("Geometries deleted.")
         else:
             self._write_success("No unattached geometries found.")
         self._break_line()