Prevent unnecessary writes on sales orders

When the exceptions are the same, do not write them again,
this prevent to write on sales orders when it is not necessary.
Column name is exceptions_ids, not exception_id
Fix 3 pep8 errors is sale_dropshipping
[IMP] add multi-company support in module sale_exceptions
[FIX] faulty default function signature
add .mailmap to fix authors for git-shortlog
[FIX] The description has to be changed only if flag set as False according what was done in other modules (see e.g module 'sale')
[FIX] typo
[FIX] Replaced description by description_sale because the latter is that used in sale order
Merge pull request #35 from tafaRU/7.0_fix_sale_line_description

[FIX] module 'sale_line_description'
Merge pull request #33 from yvaucher/7.0-add-mailmap

add .mailmap to fix authors for git-shortlog
sale_validity: backport 8.0 tests to 7.0
Fix the tests on OCB branch (closes #37)

The test failures of sale_exception_nostock on OCB branch are caused by
https://github.com/OCA/OCB/commit/5d795c48fb394505d5a6bbf77961d63da05515c4
which changed the date considered for the stock moves from `date_order` to
`date_confirmed`.

In order to restore the test behavior, we mock `datetime.now`
which is ultimately used in `sale_order.action_wait` to write `date_confirm`.
The current date is restored after each confirmation, in order to avoid
impacting other aspects of the tests (if any).

This does not impact the test on the official branch and gives the correct
results on OCB.
Merge pull request #40 from gurneyalex/7.0-fix-sale_exception_nostock

Fix the tests on OCB branch (closes #37)
Merge pull request #31 from nbessi/sale_ex_multi_comp

[IMP] add multi-company support in module sale_exceptions
Merge pull request #17 from guewen/sale-exception-useless-write

[FIX] sale_exceptions - Prevent unnecessary writes on sales orders
Merge pull request #36 from gurneyalex/7.0

sale_validity: backport 8.0 tests to 7.0
remove call to travis_run_flake8 from .travis.yml
fix mutable object as method arg default value

use states=None in sale_order.action_invoice_create() which is interpreted in
the parent class implementation as meaning ['confirmed', 'done', 'exception']
Merge pull request #45 from gurneyalex/7.0-fix-pylint

fix mutable object as method arg default value