However, this still returns 0s for some reason.

This commit removes the `servant-static-th` dependency from the project,
because it turns out we weren't using this package, and furthemore we
were depending on a fork of the latter.

We were depending on Alexandre's fork of `hstatistics`, but in the
meantime his changes got merged upstream and the maintainer release
version `0.3.1` on Hackage, so this commit changes the `stack.yaml` file
to use that.

On Mac, building `gargantext` requires linking against the
Accelerate framework (completely unrelated to the `accelerate` Haskell
package!). This patch provides an extra `pkgs.nix` directive that will
kick in only when building on Darwin.

They are changed to MaybeFields ...Read instead when joining.

Remove joins, use optionalRestrict instead.

Also, remove cabal.project because stack.yaml and package.yaml cover
dependencies already.