[FIX] web_tip: prevent useless calls to eval_tip
[FIX] web_tip: properly remove the tip popover
[FIX] doc: double period in footer
[FIX] doc: incorrect class access in new api guide

When creating a class with the new API, we should use models.Model
instead of just Model.

closes #3713
[FIX] website_forum: use common method to compute tags for orm
[FIX] im_chat : momentjs undefined on external pages. Temporary fix by replacing moment() by window.moment(). The moment helper is defined in core.js, which is not imported in web_assets common. If refactoring, the dates will be pre-process in render_messages().
[MERGE] forward port of branch 8.0 up to fc329b6
[MERGE] forward port of branch 8.0 up to c41109f
[FIX] Add missings files from previous forward port.
[FIX] event: fixed call to _check_auto_confirmation
done as api.one -> take first item in result list.

A test has been added; registrations were always automatically confirmed
even when auto_confirmation parameter was False.
[IMP] website_event_sale:  'Validation of seats availability in cart'.
Attendees are created and deleted on changing the quantity from the cart.