Joao P Dubas a69b771847 [extra-01] training has a period validity
We move from start/end date to a period date range to represent the
interval where a training take place.

Besides that, new constraints are added to ensure a trainings of a user
can't overlap. These constraints reflect in changeset validation.
2021-06-28 00:31:36 +00:00
..
2021-06-22 01:55:16 +00:00