* [8.0][mass_mailing] some fixes
* [FIX] rename wrong mailing_type field and add missing fields when creating a mass mailing from the composer
* [FIX] coerce tooltip to an unicode string to avoid a json crash when locale produces a non unicode string for strftime(%B)
* [FIX] repair wrong sql statement computing statistics
[REVERT] web: fixed css of hidden input file: could not click on add attachments anymore

This reverts commit 4e32b9f6f32eea0e4a5bb9d83c5c5f45f775f799.
[FIX] osv/fields.py: enable argument 'obj' in property fields

Fixes #1719
[FIX] web: grid headers should be aligned properly
[FIX] css fix in graph view

The field selection menu was not positioned correctly when there was
a long list.  (was not displayed at the position clicked)
[FIX] mail: when checking for possible messages to fetch, perform
a search_count on mail_message when the actual number of messages or their
ids is not necessary, to speedup the computation.
[FIX] [IMP] mail: mail_message: when checking that access rights are not
violated in _search, do it in SQL to speedup the query. Indeed doing it via search and
browsing the results to validate the various rules is quite costly.
[REVERT] commit 5e5c73e

Branch 8.0 is a **stable** branch. This mean no database schema
changes.
[FIX] fetchmail: do not delete a failing email when using POP

In case of IMAP, the email is simply set as read but in case of POP, the email is deleted. To avoid loosing data (e.g. misconfiguration of server), the email is kept for POP.
Bug lp:1296724, opw 605667
[FIX] product: don't display 'create and edit' option on many2many_tag to create variant on product_template. The quick create is confusing for users
[FIX] crm, hr_recruitment, task, issue: fixed default priorities + order based on priority (desc for everyone now)
[IMP] models: move prefetching of records back to method _prefetch_field

The selection of records in cache for prefetching was moved to method
_read_from_database() by xmo at rev 785018cc in order to fix an access right
bug.  But this introduced an issue: to explicitly avoid prefetching, you should
use read() instead of browsing records.  We revert the change by xmo, without
reintroducing the bug (which apparently was fixed by another way).
[FIX] point_of_sale: generate bank statement with commerical partner

When a pos session is closed & confirmed, the account.move were generated with the commercial partner except for the bank statement which prevented automatic reconciliation.
This patch uses the commercial partner also for bank statement.
Fixes #1558, #1764
[IMP] stock: stock incoterm converted to uppercase
[ADD] doc: new documentation, with training tutorials, and new scaffolding
[IMP] doc/howtos/backend: use scaffolding and adapt text and code accordingly
[FIX] Make sure packages are not shown when the setting is not checked
[IMP] No propagation when destination move is done/cancel
Merge pull request #1776 from acsone/8.0-jne-mass_mailing-improvements

[FIX] Mass mailing: fixed statistics computation + summary graph tooltips (using ustr) + values of the mass mailing when creating it from the mail composer wizard. Courtesy of Acsone.
[IMP] doc/howtos/backend: add a small section on how to start the server