cubicweb-timeseries #191582 support shifted calendars [resolved]

we want to be able to describe calendars in which the beginning of the year and the beginning of the day are shifted from an existing calendar.

Eg : year goes from Oct 1st to Sep 30th, and days go from 6AM to 5:59:59 AM (the next day). With such a calendar, yearly aggregation use the shifted definitions (year start on Oct 1st, 6AM and ends on Oct 1st 5:59:59 the next year), and daily, weekly, monthly aggregations use the shifted day definition.

done in1.0.0
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