Allow special characters as Create text file input

[wm75]

This change allows arbitrary characters as tool input without compromising safety against malicious text.

The added test revealed a bug in the existing tests, which only tested against default settings.

The newly added "sanitize_text" macro may be useful for other tools here, too.

[bgruening]

Do you want to add this sanitizer to the other tools as well?

[wm75]

I'm planning to (that's why I put it into the macro file), but not in this PR.

Actually, the other tool I'd be interested in fixing soon is add_line_to_file, which lives a level higher in its own directory so using the same macro is not possible unfortunately.