New schema for the GeoModel SQLite database and updated I/O

==> NOTE: This is a follow-up MR of !317 (closed).

I had to rebase the branch used in !317 (closed) onto main to fix errors raised in the rebase step of the Athena build. But that caused a deep rewrite of the commit history of the original development branch. To avoid affecting the original branch and to remove unnecessary clutter, I renamed the rebased branch and opened a new MR. So, we can test the new rebased branch in the Athena build without modifying the original development branch.

For all details and changes, see the description and the comments of !317 (closed).

Cc: @tsulaia and @boudreau