[11.0][web_timeline] add_events function is called many times

[ruben-tonetto]

When i move a gantt bar, _render() function is fired, so add_events() function is called.
Every button (today/day/week/...) receive a new click event, but the previous click event is not cancelled

i think add_events() should be put in start() or add jquery off('click')

[tarteo]

@ruben-tonetto Thanks, I've created a PR to fix this issue. Next time don't be shy to create a PR yourself 😊