Fix QML warnings

There are quite a few QML layout warnings.

changed milestone to %Itération 21

mentioned in commit d4c5f422

mentioned in commit c5687508

mentioned in commit a79bf21a

closed

mentioned in issue #573 (closed)

mentioned in issue #631 (closed)

mentioned in issue #718 (closed)

mentioned in issue #772 (closed)

mentioned in issue #929 (closed)