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/de.ts

@@ -753,6 +753,7 @@ export const catalog: Catalog = {
     "Attachment reminder": "Anhang-Erinnerung",
     "Warn when the message mentions an attachment but none is attached.": "Warnen, wenn die Nachricht einen Anhang erwähnt, aber keiner angehängt ist.",
     "Spell check while typing": "Rechtschreibprüfung während der Eingabe",
+    "Open the composer full screen": "Nachrichten im Vollbild verfassen",
     "Confirm before deleting": "Vor dem Löschen bestätigen",
     "Show message snippets": "Nachrichtenvorschau anzeigen",
     "Preview the first line of each message in the list.": "Die erste Zeile jeder Nachricht in der Liste anzeigen.",