Scripts: Disable markup in error messages

Error messages are displayed using the following methods:

* **zenity** parses pango markup and replaces escaped characters
* **kdialog** replaces (some) escaped characters
* **gtk-dialog.py** replaces `\n`
* **printf** interprets format strings and replaces escaped characters
* **echo** just displays the text

The error messages themself contain escaped characters and paths from variables.

This PR unifies the behavior by:

* Use **printf** to format error messages and replace escaped characters
* Setting `--no-markup` for **zenity** to disable pango markup and escaped characters
* Remove `\n` replacement from **gtk-dialog.py**.
* Use plain **echo** instead of **printf**

packaging/linux/gtk-dialog.py

@@ -43,6 +43,6 @@ if __name__ == "__main__":
     parser.add_argument('--text', type=str, required=False, default='')
     args = parser.parse_args()
     if args.type == 'question':
-        Question(args.title, args.text.replace('\\n', '\n'))
+        Question(args.title, args.text)
     elif args.type == 'error':
-        Error(args.title, args.text.replace('\\n', '\n'))
+        Error(args.title, args.text)