[ENH] refactor events data and page creation

[Remi-Gau]

closes #7

AIM

• have all info about all events centralized in a single yml

should facilitate reuse of event info from year to year, or if we need to move to another framework

• have a simple "switch" for each event to display it or not

if an event is not happening on a given year we can just turn it off

• adapt page generation code accordingly (remove the one page for each event)