This commit removes the dependence to website_legal_page by using it's
own template for showing text aside the checkbox in the form. Because
the template for this text is not editable by the user (in fact, it is
but each time the module is updated, this template is overwritten).
Of course website_legal_page can always be installed, and the new
template for the text can contain link to the pages generated by
website_legal_page.