to prevent n_jobs <=0

* Catching exceptions to have error messages inside ZOPE rather than timeout
* Fix timeout bug when timeout is None
* Preparation for the the two-stage computation when the transaction is aborted
  retried when all the jobs have finished running.

In the report code, this at_date is used and report generation would
fail if user does not select an `at_date`.

/reviewed-on nexedi/erp5!448

This merge request contains the feature to login in ERP5 with Google Account.

Also, this branch is based on the work done in nexedi/erp5!185

We have a lot of discussion about this changes in nexedi/erp5!179, but with a lot of merge conflicts, a new MR is better to review.

This branch will wake up the discuss of "Moving API Keys from preference to a better place", I can work on it but I am not sure if we have a good design yet.

Any comment is welcome

/cc @tb @romain @rafael @kazuhiko @vincent @jerome

/reviewed-on nexedi/erp5!219

/reviewed-on nexedi/erp5!441

/reviewed-on nexedi/erp5!444

erp5_trade: Fix Order and Packing List print to use Proxyfields not in Meta forms Hide whitespace change

This prevent to have printout failing when erp5_mrp_item is installed
as it extends Base_viewTradeFieldLibrary but do not contain the fields
for these printouts.

Also, do some trivial cleanup

/reviewed-on nexedi/erp5!435

/reviewed-on nexedi/erp5!434

/reviewed-on nexedi/erp5!432

Rework Balance Sheet and Profit and Loss so that they are more consistent with other reports:
 - Ability to choose output format and produce in deferred mode
 - Allow specifying the date range explicitly, for current period and previous period as well. When dates are not specified, the previous behavior of guessing start date and previous date range from accounting periods is kept
 - Style fixes
 - Set a filename for *Save as ...*

Introduce a new feature on Profit and Loss to allow to have instead of the two column layout (used in France mostly):

| INCOME  | EXPENSE |
|---------|---------|
| **1. Revenue** | **1. Operating Expenses** | 
|     - ...... | - ...... | 
|    | - *Cost of Sales* | 
|     | - *Selling, General and Administrative Expenses* | 
|     | - *Other* | 
| **2. Non Operating Income** | **2. Non Operating Expense** | 
|     - ...... | - ...... | 
| **3. Interest Income** | **3. Interest Expense** |
|     - ...... | - ...... | 

Have a one column layout with intermediate profit/loss calculated for each level ( what I call "british layout" here):

| Profit and Loss  |
|---------|
| **1. Operating** |
|  * *Sales* | 
|  * *Operating Expenses* | 
|        - ...... |
|        - Cost of Sales | 
|        - Selling, General and Administrative Expenses | 
|        - Other | 
| **2. Non Operating** |
|  * *Non Operating Income* | 
|        - ...... | 
|  * *Non Operating Expense* |
|        - ...... | 
| 3. **Financial** |
|  * *Interest  Income* |
|        - ...... | 
|  * *Interest Expense* |
|        - ...... | 

This is achieved by putting all that hierarchy in `portal_categories/financial_section/income` and not splitting it in `income` and `expense`. This report will not display `expense` category if it is empty.

Still TODO:
* [x] updating https://www.erp5.com/erp5-HowTo.Select.Accounting.Financial.Section

/reviewed-on nexedi/erp5!284

Making "modified_object_list" consistent by always containing tuples and not
sometimes lists and sometimes tuples.

Also, update the files where they have been used

Using _getOb is always less costly than getattr, as it reduces the need to look in acquisition.

And simplify manage_exportProperties function accordingly

Also, we don't need to look for `transactionless` connection-id here,
as we don't use them in catalog methods.
And, update the files where we can use the new function.