This caused two problems:
 - If Xfvb was killed and left a stale lock file, we don't reuse this
   display. After some time we end up having "All display locked"
   exception but no Xvfb process running.
 - Xvfb's slapos is patched to store control sockets and lockfiles in
   $TMPDIR ( nexedi/slapos@58462c24 ).
   We don't have $TMPDIR set in testnodes, but this would be a problem
   if we ever set it.

Because Xvfb can detect a stale lock file upon startup and start anyway,
the easy way running Xvfb for each display and see if it's still running
after a few seconds.

@Tyagov 
 
Added a test to check int64 and float64 Numpy arrays because an error like this existed before:

```
in Base_executeJupyter
     return json.dumps(result)
   Module json, line 244, in dumps
     return _default_encoder.encode(obj)
   Module json.encoder, line 207, in encode
     chunks = self.iterencode(o, _one_shot=True)
   Module json.encoder, line 270, in iterencode
     return _iterencode(o, 0)
   Module json.encoder, line 184, in default
     raise TypeError(repr(o) + " is not JSON serializable")
TypeError: array([[ -245554.,    19410.,  1453313.],
        [ -238947.,    18888.,  1443651.],
        [ -238416.,    18350.,  1444382.],
        ...,
        [ -250816.,    19482.,  1445528.],
        [ -251464.,    18678.,  1444711.],
        [ -253475.,    18786.,  1444842.]]) is not JSON serializable
```

/reviewed-on nexedi/erp5!285

/reviewed-on nexedi/erp5!290

/reviewed-on nexedi/erp5!287

At and From should not be title cased in "Previous Period At/From Date"
message.

By adding returned_purchase_packing_list_builder and
purchase_packing_list_builder to Alarm_buildPackingList they are used in
tested alarms.

Returned Purchase Packing List and Returned Sale Packing List can be
generated by corresponding orders.

Test are based on testOrder logic and assertions.

By adding Returned Purchase Order and Returned Sale Order it is possible
to operate with reverse logistics: return the goods sold or purchased.

@Tyagov @luke 

See the MR at slapos [here](nexedi/slapos!177).

/reviewed-on nexedi/erp5!283

this is used for file name to download

This report has always been based on "french layout", where there is first
all expenses on one page and all incomes on next page.

In the "british layout", there is only one sheet, showing income -
expense on the same layout ( as we can see today on
 https://en.wikipedia.org/wiki/Income_statement#Sample_income_statement
)

The idea is that we can configure financial section either with two
hierarchies for expense and income to have the french layout, or put all
the "british layout" hierarchy in income and leave expense empty.

(Just moving code arround to prepare next commit)

( see existing styles in Base_getODSStyleSheet )

Exchange action are meant to import/export a list of documents

https://w3c.github.io/server-timing/#the-server-timing-header-field

 ... this js was already included

Reuse code of delivery to ensure we can customize which item should be
in item table

This reverts commit 2ef67082

This allow customization, original init script is called by new script.