[IMP] *: convert to private methods

render, render_template, load, activity_schedule_with_view,
get_website_pages should all be private:
It should not be possible to render an aribtrary template only with
its name or id

Still need to render some qweb views from js so the method
render_template is kept public.
This explains why the website editor still need read access on
ir.ui.view as we want to allow any snippet to be rendered.