CMFActivity: Remove transaction.commit and sleep from initial implementation and use conflict error instead

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.

[erp5_core] Remove quantity input field from category view form. Do not input quantity on category and use quantity unit conversion module instead.

[erp5_configurator_standard_categories] Use quantity unit conversion module to define quantity of category and stop using quantity property on categories.

To take into account organisations with multiple establishments and module containing DSNs for other organisations

Only quantity should be set

Proof is indeed it already changed

And update the related view

/reviewed-on nexedi/erp5!544

This reverts commit e1fa7611.
The fix was already provided by c1b8fa1a

Firefox doesn't display new line with: white-space: normal

replication test