Replace the year of a date is not safe, it is better to use relativedelta.
Closes#13064
(grafted from 4b19fb0bc801a784139c0c6245d8649480e13280)
--HG--
branch : 7.0
When a new parent is added to a tree template like types, taxes or tax codes,
the corresponding record of the new template parent is not yet created.
So we need to use a default value for the parent and update again the tree
after creating the new records.
Closes#12755
(grafted from 561f9c7dbdc2a2c39c1fe5f6bf7274d01ee9ebd6)
--HG--
branch : 7.0
The fiscal years are created centered on the passed date such that if the
current day change during the execution, the fiscal year is still usable.
Also fiscal year can be created for a range of dates such that it is guarantee
that the dates are in the fiscal year.
And finally remove datetime and dateutil import when they are not used.
Closes#9977
Cédric Krier