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**
This explicitly tells KDE to associate the OpenRA window with
the integrated appimage desktop file, allowing it to use the
correct resolution icon for the task switcher.
This removes the "View FAQ" button, which does not work in the AppImage
enivronment. It also replaces the inconsistent question mark icon with
a more appropriate stop symbol, and makes the wording consistent across
the zenity, terminal, and native macOS dialogs.
