The bottom of event is shared between all event page and all events.
This is especially misleading when "website menu" with
website_event_track is activated on the event, then we will have several
pages such as "Introduction" / "Location" and depending on if we drop a
widget some pixel too high or two low, it will be only on the current
page or on all events.
With this changeset, when editing there is an information block saying
what part is on all page.
opw-2002163
closes#33857
Signed-off-by: Nicolas Lempereur (nle) <nle@odoo.com>