Consistently use URIBASE / ONTBASE

Nobody has claimed this yet.

The standard Makefile has three very similar variables:

* `OBOBASE` (hardcoded to `http://purl.obolibrary.org/obo/`);
* `URIBASE` (set to the project’s `uribase` setting, defaulting to `http://purl.obolibrary.org/obo/`);
* `ONTBASE` (set to `URIBASE` + either the project’s `uribase_suffix` setting or its `id` setting).

Within the Makefile, `URIBASE` is mostly used whenever we need to use ROBOT’s `--base-iri` option, while `ONTBASE` is mostly used to set the ontology IRI and the version IRI.

However we are not entirely consistent, for example:

* Most of the import pipeline actually uses either
* `{{ project.uribase }}` directly instead of the `URIBASE` variable, or
* `$(OBOBASE)/something` – that one is particularly problematic as it basically hardcodes the fact that an import is assumed to be an **OBO** import.
* The main release artefact (`$(ONT).owl`) is annotated with an ontology IRI of `$(URIBASE)/$(ONT).owl` instead of `$(ONTBASE)/$(ONT).owl` – presumably this is on purpose, to reflect the OBO convention that the main release artefact (the artefact that is not qualified with any “variant” suffix) is expected to be found at `http://purl.obolibrary.org/obo/$(ONT).owl`, while “qualified” released artefacts are expected to be found at `http://purl.obolibrary.org/obo/$(ONT)/$(ONT)-qualifier.owl`.
* When producing the main ROBOT report, we are using `$(URIBASE)/{{ project.id }}` and `$(URIBASE)/{{ project.id.upper() }}` – thereby ignoring the project’s `uribase_suffix` setting.

We need to be much more consistent here. In particular, I’d argue that we should _never_ use `$(OBOBASE)` – in fact, that variable should not even exist in the Makefile in the first place.

Start with the standard Makefile and trace every use of OBOBASE, URIBASE, and ONTBASE, including the import pipeline, release artefact, and ROBOT report rules. Compare those uses with the project uribase, uribase_suffix, and id settings. Done means the variables are used consistently, OBOBASE is removed, and the intended ontology and version IRIs remain correct.

Written by the indexing model from the issue text.