Follow a simple / non-simple approach, like for Task and its lines.

In default case, user would need only one Leave Request Period, which
can be edited directly on LeaveRequest_view. So, in this case, hide the Listbox
containing the Leave Request Periods and have default_leave_request_period
being created / edited on background, which will acquire quantity, resource, start_date and stop_date
from what is set at the view of the Parent.

In case one or more Leave Request Period are added manually, user would get
listbox with sub-objects, and editing should be done directly on them, i.e. fields like
my_default_leave_request_period_start_date will be disabled from LeaveRequest_view.

Additionally, now Leave Request has it's own:
- start_date: equal to the minimum start_date of all Leave Request Periods
- stop_date: equal to the maximum stop_date of all Leave Request Periods

These values are set by interaction on Leave Request Period, triggered on
_setStartDate, _setStopDate. This helps so that leave_request_module listbox
can have sortable dates.

Commit contains also <a href="https://lab.nexedi.com/georgios.dagkakis/erp5/blob/leave_request/product/ERP5/tests/testCalendar.py#L1626">test</a> that should make it easier to understand.

Test results <a href="https://nexedi.erp5.net/test_result_module/20171113-20E90B8F">here</a>

@seb we have talked on this and @cedric.leninivin I know you dealt with Leave Requests. Who else should be notified?





/reviewed-on nexedi/erp5!493

ERP5 doesn't provide any information about the timezone used internally.
As test doesn't know the selenium browser locale, full text can't be checked.

[erp5_core, erp5_property_sheets, erp5_pdm] Add time_quantity_unit and order_quantity_unit categories and add max/min order quantity to supply. Also cleaning up proxy fields for supply view forms.

After migration of catalog to ERP5-ified document, its better to migrate all the catalog methods (`ZSQL Method, Python Script`) to new format. This will save the 
time during migration for developers and will reduce the chance for error during *import_in_old_format >> export_in_new_format* process.


Some important changes during re-export:
- Classes for new catalog methods are now defined via `portal_type`
- Filter is now defined via properties, so no need to save their properties in `.catalog_keys.xml` file.

/reviewed-on nexedi/erp5!518

erp5_pdm: use preferred category child item list method in my_variation_category_list field library.