[ADD] website: add new page management

website.page = old ir.ui.view with page=True
website.redirect is a new mechanism to replace in the futur the ir.attachment
mechanism of redirect.

From now, we don't have a specific /page controller to serve 'page'.

We use a new model website.page which is rendered if none route matches the url
 and that the field 'url' on website.page matches the request.httprequest.path.

The order to serve a path is:
    - Routes defines in controllers (/shop, /blog, ...)
    - ir.attachment with name matching the path
    - website.page with url matching the path
    - website.redirect with url_from matching the path
    - 404

To improve:
    - allow regexp in website.redirect model
    - allow to edit the view_arch from the page.management via redirect backend
      (needed when traceback in the page, or when modifying a js/css/less/...)