[erp5_officejs] Replace devellopement for global gadget by app and change signature storage for erp5 sync

Following up !308 , these are a batch of changes to fix coding style in `erp5_accounting` as reported by pylint and `Products.ERP5Type.CodingStyle`.

Also, calls to `portal_catalog.getObject` are replaced by simple `portal_catalog` calls.


/reviewed-on nexedi/erp5!309

In `sheet_per_report_section` mode if the report do not have any fields,
we use to display an empty sheet. It was confusing and not useful.

This export action produce a spreadsheet containing information needed to physically prepare sales packing lists, prepare a mailing to prepare address stickers or whatever specific processing "outside of ERP5" can be needed when sending sales packing lists.

It is an action on sales packing lists module:

![Screenshot_2017-07-10_at_14.30.10](/uploads/554a0d7b656aaa88d250136dd39309f3/Screenshot_2017-07-10_at_14.30.10.png)

Offering two level of details:
 * One line per sales packing list line
 * One line per delivery, with the resource / quantities "packed" in a column

Both versions will display a list of sales packing lists, but only the one where resource is a product. The idea is to only care only about physically delivered goods.

When requesting boths (which is the default), user will get a spreadsheet with two tabs, like this example: [Shipment_Report.xlsx](/uploads/c39906f36cbddd5c20cdd4ce39a90381/Shipment_Report.xlsx) (this is using data from `testTradeReports.TestTradeReports.testShipmentReport` added in this MR)

The intended use case of this action is to select packing lists to prepare (usually with worklist), export this spreadsheet and change state of the selection.

/reviewed-on nexedi/erp5!320

/reviewed-on nexedi/erp5!345

/reviewed-on nexedi/erp5!343