Usually we run tests with two nodes, so when there's a conflict it's
always between the "main" node and the processing node, so we always
have a distributing node during conflict.

But when running with, for example, 2 nodes (the main node + 2 nodes),
the conflict might occur between the two processing nodes and after
the resolution we still don't have a distributing node.

When looking up a document by reference, using getDocumentValueList from
the context of a web site / web section might not find the documents,
depending on the predicates defined on the web site / web section.

This gadget looks up a document by reference, by using
getDocumentValueList on the context of the web section.
getDocumentValueList also applies the criterions from the context, but
because web page references are already unique, adding more criterions
can just cause the document to be not found and the gadget to display
the "No document" error.

This sort was based on the id of the role definition but this did not
work when the type definition had more than 10 documents, because:

    >>> sorted(['1', '2', '10'])
    ['1', '10', '2']

This switches to an approach of converting the id to integer, with a
fallback in case the id generator is customized.

See merge request !1732

See merge request !1731

cause by !1726

On the way to Zope 4, the biggest change was DateTime >= 3, which has these main differences:

 - `DateTime` instances are new style classes
 - `DateTime.__eq__` now take into the timezone into account
 - `DateTime` supports timezone naive ( https://docs.python.org/3/library/datetime.html#aware-and-naive-objects ) - actually this is since DateTime 2.12 , but since we fully patched the method where the parsing happens, ERP5's patched DateTime never used timezone naive dates.
 - pickles are also different.

These are changes to prepare ERP5 code base to support DateTime >= 3, while keeping compatibility with the previous behavior, this means that we keep patching to keep the same behavior as DateTime 2, so that `DateTime.__eq__` ignores timezone difference and `DateTime` does not support timezone naive dates - these two different behavior seemed to introduce too much breakages, especially in project code, with no immediate benefit for our usages. For now, while ERP5 is still based on Zope 2 / DateTime 2 the fact that DateTime are new style classes has no impact, this will only impact once we switch to Zope 4.

This also change the code to adjust the part where we were depending on implementation details of DateTime and where the details changed on DateTime 3, sometimes exposing higher level API, like the new `timeZoneContext` to use in tests.



See merge request !1593

See merge request nexedi/erp5!1725

See merge request nexedi/erp5!1726

use calendar module and public DateTime API instead.

This ensures that we don't break more.

We have code depending on these attributes, they were used in pattern
like this:

```py
try:
  DateTime(user_input)
except DateTime.DateError:
  error("invalid date")
```

so it's safer to keep the attributes for now, since we are already
patching a lot

We have too much code depending on this behavior, so we keep this patch
for now.

By using iso format we create dates in UTC timezone

This is a context manager which temporary allow to change the time zone.

It is not thread safe and intended to be used in tests only, to replace
setTimeZoneToUTC and setTimezone methods by something unified which
makes the transition to DateTime 4 easier, because changing timezone
was done by patching private attributes and the DateTime 4 use different
attributes.