Cleanup VIEW definition NULLS LAST is not necessary on non-nullable columns; avoid materializing unused columns in a CTE; use boolean value directly instead of comparing to auto-casted string; gauge_measurements might contain not only waterlevels; avoid unnecessary subselects.

The gemma database schema requires PostgreSQL >= 11.

`dot.tmpl` is a template file for `postgresql_autodoc`
to be more similiar to UML and leave out some less useful labels.

See  `../docker/README.md`