Adding option for user choose clean introtext on Module Articles Category

This is an small contribution to give the users ability to choose if the introtext should be cleaned or not.

This module has the ability to show basic content, but I believe that would be nice for user wants to show the clean content or leave as was posted, opening more possibilities on how to use this module... I already needed to display full content using this module and always need to do overrides, so, adding this small contribution, would avoid the override
Should be `$params->get('clean_introtext', 1);` :smile: