Implement save method for strings

[ctrueden]

This plugin should be able to save a String as plain text to a .txt file when requested. See also this forum thread.

[imagesc-bot]

This issue has been mentioned on Image.sc Forum. There might be relevant details there:

https://forum.image.sc/t/using-textioservice/70207/6