feat: multiple improvements to the Studio-Web app in both fr and en

[joanise]

• revised a number of French translations
• all external links now load in separate tabs to avoid resetting the app
• the space just inside « and » needs to be non-breaking to avoid dangling quotes
• make the privacy policy dialog wider for more pleasant reading experience (it still auto-shrinks on small devices, so this is still properly responsive)
• modify the Text format help popup to be more similar to the Privacy popup, with a Close button at the botton and only one title line

[dhdaines]

Looks good, but do we want to continue to avoid saying "Upload" / "Téléverser" ?