Log Message:
retext: updated to 7.2.1

ReText 7.2.1

* Improved support for dark Qt themes.
* Fixed preview jumping to top during MathJax rendering.
* Fixed QTextBrowser-based preview jumping.
* Fixed opening files with spaces from QTextBrowser-based
  preview.
* Use `defaultCodec` setting by default when saving files;
  correctly detect encoding for UTF-8 files with BOM.