feat: support importing emails from .zip archives

locales/zh/common.json

@@ -270,7 +270,7 @@
     "print": "打印",
     "view_source": "查看源码",
     "export_email": "导出为 .eml",
-    "import_email": "导入 .eml",
+    "import_email": "导入 .eml 或 .zip",
     "keyboard_shortcuts": "键盘快捷键（？）",
     "email_source": "邮件源码",
     "draft_banner": "这是一封草稿邮件",
@@ -1794,7 +1794,7 @@
     "new_subfolder": "新建子文件夹...",
     "new_folder": "新建文件夹...",
     "rename": "重命名...",
-    "import_email": "导入 .eml...",
+    "import_email": "导入 .eml 或 .zip...",
     "empty_folder": "清空文件夹",
     "empty_folder_generic": "清空文件夹",
     "delete_folder": "删除文件夹",