Error in EventsDict init with duplicated key events

When creating a EventsDict from a list of Events with the same key, only the last one is stored:

EventsDict([
    EventWindow('FOO', t_start='2035-01-01', t_end='2035-01-02'),
    EventWindow('FOO', t_start='2035-01-03', t_end='2035-01-04'),
])

	event	#	t_start	t_stop
0	FOO	-	2035-01-03	2035-01-04

This is related to EventsDict.__init__() that overwrite the event key:

def __init__(self, events, **kwargs):
    self.data = {
        event.key: event
        for event in sorted(events, key=attrgetter('start'))
    }

If a key is duplicated, the events should be stored in an EventsList.

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Catched by @nmanaud.