Merge public ihasmail: folder reordering, full-screen composer, Dutch update

- Reorder folders by dragging, with special folders first (#402, #405).
- Open the composer full screen, as a setting (#401, #404).
- Dutch translation update (#403).

FEATURES.md stays deleted here, as in bb25355.

web/src/locales/fr.ts

@@ -754,6 +754,7 @@ export const catalog: Catalog = {
     "Attachment reminder": "Rappel de pièce jointe",
     "Warn when the message mentions an attachment but none is attached.": "Avertir lorsque le message mentionne une pièce jointe alors qu'aucune n'est jointe.",
     "Spell check while typing": "Vérification orthographique pendant la saisie",
+    "Open the composer full screen": "Rédiger les messages en plein écran",
     "Confirm before deleting": "Confirmer avant de supprimer",
     "Show message snippets": "Afficher un aperçu des messages",
     "Preview the first line of each message in the list.": "Afficher la première ligne de chaque message dans la liste.",