Feature: Add request all languages unit test

[syphax-bouazzouni]

Context

This PR adds the final modifications and tests for the Multilingual topic (https://github.com/agroportal/project-management/issues/307) done in the PRs below:

• https://github.com/ontoportal-lirmm/ontologies_linked_data/pull/91
• https://github.com/ontoportal-lirmm/ontologies_linked_data/pull/85
• https://github.com/ontoportal-lirmm/ontologies_linked_data/pull/83
• https://github.com/ontoportal-lirmm/ontologies_linked_data/pull/80
• https://github.com/ontoportal-lirmm/ontologies_linked_data/pull/73
• https://github.com/ontoportal-lirmm/ontologies_linked_data/pull/71
• https://github.com/ontoportal-lirmm/ontologies_linked_data/pull/67

Changes

• Fix the class portal language test for the new multilingual support (https://github.com/ontoportal-lirmm/ontologies_linked_data/pull/93/commits/e1b9af7a7ba6877554d58c3d8145ef55c21ec3e9)
  • Now when we ask a language we ether the values with the matching language, or nil or empty if not. Before we had a fallback to show the values in the other languages to not have empty fields
• Fix SKOS Xl tests after the new multilingual support (https://github.com/ontoportal-lirmm/ontologies_linked_data/pull/93/commits/6825393c658609dafee9638df9ae31e35b173f89)
  • SKOS XL labels are tagged with a language so the literal value is empty if it does not match the requested language but the object is still fetched and showed
• Optimize request and portal lang tests by parsing the test ontology once](https://github.com/ontoportal-lirmm/ontologies_linked_data/pull/93/commits/09a3f4884946b261c5dcf15fd3be2285e3afa84d)
• Add test request all languages unit test](https://github.com/ontoportal-lirmm/ontologies_linked_data/pull/93/commits/56b88e6ec66887ee783d0263e9c80800b000ab98)
• Use the new getters argument to show languages](https://github.com/ontoportal-lirmm/ontologies_linked_data/pull/93/commits/707b69d37ac3d692bed0e466474d015d0aa64c57)