Reasons for creating this PR

Vocabularies that didn't have a label in the current UI label were not visible on the landing page. See #1824

This PR fixes the problem by adding a fallback: if a vocabulary doesn't have a dcterms:title in the current UI language in the config.ttl file (and also doesn't have a title without a language tag), then Skosmos will just pick any title regardless of the language tag. This ensures that the vocabulary is visible, even though its name may not be in the expected language.

The change also affects the vocabulary dropdown list in the global search bar: now vocabularies without a title in the current language are also shown in that list. (This caused some breakage for Cypress tests that didn't expect this.)

Link to relevant issue(s), if any

• Closes Don't hide vocabularies with missing title #1824

Description of the changes in this PR

• implement fallback for VocabularyConfig::getTitle
• add a PHPUnit test that verifies that the fallback works
• adjust some Cypress tests related to the global search bar that broke due to this change

Known problems or uncertainties in this PR

none

Checklist

• phpUnit tests pass locally with my changes
• I have added tests that show that the new code works, or tests are not relevant for this PR (e.g. only HTML/CSS changes)
• The PR doesn't reduce accessibility of the front-end code (e.g. tab focus, scaling to different resolutions, use of .sr-only class, color contrast)
• The PR doesn't introduce unintended code changes (e.g. empty lines or useless reindentation)