TXT Export Indentation on lists Edit

* We don't allow plugins to apply filters to exports, this would be nice in the future maybe..
* Please ensure I didn't leave any cruft in from HTML export method.
* Please check security as I no longer security escape chars before exporting to pads.
* I do a bad fix on stopping evil chars from plugins so a line that has text content that is purely a * wont export.

Tested numbered, indented (multiple), ep_headings and bullet