feat: support importing emails from .zip archives

locales/da/common.json

@@ -270,7 +270,7 @@
     "print": "Udskriv",
     "view_source": "Vis kilde",
     "export_email": "Eksportér som .eml",
-    "import_email": "Importér .eml",
+    "import_email": "Importér .eml eller .zip",
     "keyboard_shortcuts": "Tastaturgenveje (?)",
     "email_source": "E-mail-kilde",
     "draft_banner": "Denne besked er en kladde",
@@ -1794,7 +1794,7 @@
     "new_subfolder": "Ny undermappe...",
     "new_folder": "Ny mappe...",
     "rename": "Omdøb...",
-    "import_email": "Importér .eml...",
+    "import_email": "Importér .eml eller .zip...",
     "empty_folder": "Tøm mappe",
     "empty_folder_generic": "Tøm mappe",
     "delete_folder": "Slet mappe",