This merge adds the website_visitor model that will be used
to track website visitor activity (page viewed, number of visits and
more general info about the visitor (country, lang, etc..)

This model will, in later commit, be used to send chat requests
and push notification from the operators (or backend users)
directly to the visitor.

To keep a detailed history of the visitor page views,
we add a website.visitor.page model that makes the link
between visitor and website.page but that keeps the visit date.
So that we can see if a visitor went mulitple times
on the same page and when. It's useful to see his last page views.

If a website_visitor submit a contact form (and becomes a lead),
the website_visitor is linked to the crm.lead.

If a website_visitor logs in,
the website_visitor is linked to the user's res.partner.

This also allows a livechat operator to send a chat request to a
connected and available website_visitor.

See sub commits for more detailed informations about functional flows
and technical changes/decisions.

Task : https://www.odoo.com/web?#id=2028059&action=327&model=project.task&view_type=form&menu_id=4720

Linked to enterprise PR odoo/enterprise#4834

This PR adds Stock Valuation Identification Method support for Warehouse Accounting.

Assume that we have

- Day 1: stock `in 2` pc @ `$100` with Seials `0001` and `0002`
- Day 2: stock `in 2` pc @ `$200` with Seials `0004` and `0005`
- Day 3: stock `in 2` pc @ `$300` with Seials `0006` and `0007`
- Day 4: stock `out 3` pc `0001`, `0004`, `0007`

### Current behavior before PR:

Odoo does not respect the serials input during delivery then it valuates only 100+100+200 = 400 (serials 0001, 0002, 0004 respectively)

### Desired behavior after PR is merged:
The out valuation should be 100 + 200 + 300 (serials 0001, 0004, 0007 respectively)

### What this PR does

1. [IMP] move methods `_create_%s_svl` from stock move to stock move line for more relevant and shorter code. It also helps later development of Valuation Identification Method
2. [ADD] fields `stock_move_line_id` and `lot_id` to stock.valuation.layer
3. [ADD] method `_run_fifo` now supports Stock Valuation Identification Method if lots are passed into the method. It does the job by
   * finding back incomming stock valuation layers having lot/serial first
   * comparing the quantity with lots with the initial fifo quantity. If the quantity with lots is less, continuing to find other candidate.
   * after these operations, the candidates with lots will be on the top of the recordset for later valuation


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