v5.21.4

This update fixes several bugs:

• The brainstorm sometimes incorrectly issued a warning about an expired session. This has now been fixed.
• In some cases, numbers with value zero were not displayed correctly when you moved over them with your mouse. This has now been fixed.
• A bugs has been fixed where switching languages sometimes led to translations in the wrong language.
• Clicking on 'remove descriptions' in the quantifier settings now actually removes the descriptions instead of only hiding them.