[ADD] website_forum_seo: add new module for improve forum que/ans description


<b>Task:</b> https://www.odoo.com/web#id=9107&view_type=form&model=project.task&menu_id=3942&action=327
<b>Pad:</b> https://pad.odoo.com/p/r.aAXbFLdZvu62soZi


<b>New Module:</b> website_forum_seo
<b>VIew Demo:</b> https://www.youtube.com/watch?v=_lYH_GrRqso

When question/answer description (HTML field) initialize to CKEditor, default CKEditor behavior ignore the all HTML elements. But in our case we need to <code>a, span</code> element that are allow to CKEditor for identify which are the replaced those are never replace again.