[runSofa] Fix DataWidget display Speicherleck and long loading

[epernod]

• Fix memory problem of GUI memory explosion in QDisplayPropertyWidget #1178
• Add mecanism to load Data vector only when clicking on "show values"

Fix #1178

---

This PR:

• builds with SUCCESS for all platforms on the CI.
• does not generate new warnings.
• does not generate new unit test failures.
• does not generate new scene test failures.
• does not break API compatibility.
• is more than 1 week old (or has fast-merge label).

Reviewers will merge only if all these checks are true.

[damienmarchal]

Bon pour le load onDemand je vote pour toi au SofaAward :)

[epernod]

non je refuse un award pour un patch sur un design de qtwidget aussi compliqué! Alors qu'il y a tellement moyen de faire simple avec qt....