Before this, the progressbar values were not updated (both count and progress)
after archiving all the records of a column.
Multiple things have been done here to update it.
Firstly, a optimization had been done to avoid reloading the progressbar when
updating a column ; this optimization was not correct due to this precise use
case. This will update the progressbar.
Secondly, the `aggregateValues` are reset when putting empty groups back in the
datapoint. This attribute is used to compute the counter if a `sum_field` is set
on the progressbar widget. It needs to be reset because the loop that computes
it won't iterate on empty groups.
Eventually, the mockRPC of the progressbar route was not taking the `group_by`
argument into account (probably a typo).
Martin Geubelle
c0809dd41d