[IMP] various improvements to the action manager (web client)

* add a replace_breadcrumb option to actionmanager
* correctly calls on_reverse_breadcrumbs when needed
* add a semi-protected way to manipulate breadcrumbs (get_widgets)
* calls do_show when changing widgets
[ADD] website_forum_seo: add new module for improve forum que/ans description
[IMP] add test cases