Add modal with a Google Meet link when clicking on an event

See merge request pbt/displaytimetable!5

# Conflicts:
#   css/timetable.css

1. remove vertical space between divs
2. make the whole header (logo + text) dismissable

of git.esi-bru.be:pbt/displaytimetable

I'm not reduce footer and header but enlarge calendar on mobile
fix #2