Before this commit printing a report would require at least two workers,
one for the original request "print this report" plus one used by the
wkhtmltopdf subprocess to download the many assets (css/js/img) present
in the html document it is rendering.

Because it was using a minimum of two workers, it was not possible to
test the rendering of PDF reports as only one worker was available for
HttpCase tests methods.

In this work, we download all assets and inline them inside the html
document prior of invocating the wkhtmltopdf subprocess so that no
further download is necessary.

task-2706552

---

**[FIX] base: 404 /web/assets during pdf rendering**

Special case for when the assets have been generated in the current
transaction, have not been commited yet and thus are not visible to
the request made with `wsgi_client` as it opens its own cursor. This
prevents the assets inlining algorithm from crashing for not found
assets.

---

*I made the extra fix commit so that it has its own commit message*

With some help from @Gorash for the unittest <3

Break down payments per tax. When creating a down payment for a sale order, create one line per tax instead of one line for the entire order.

[Sale Order]
Product    Qty  Unit price    Tax   Subtotal
Product1   1    1000          10%   1000
Product2   1    1000          5%    1000
                                    ====
                            Untaxed 2000
                                Tax 150
                                    ====
                              Total 2150

Make a 50% (1075) down payment :

[BEFORE]
Product    Qty  Unit price    Tax   Subtotal
Product1   1    1000          10%   1000
Product2   1    1000          5%    1000
Down pay   1    1075                0
                                    ====
                            Untaxed 2000
                                Tax 150
                                    ====
                              Total 2150

[AFTER]
Product    Qty  Unit price    Tax   Subtotal
Product1   1    1000          10%   1000
Product2   1    1000          5%    1000
Down pay   1    500           10%   0
Down pay   1    500           5%    0
                                    ====
                            Untaxed 2000
                                Tax 150
                                    ====
                              Total 2150

Task: 2678531

Enterprise PR: https://github.com/odoo/enterprise/pull/36331

The goal of this task is to ease the deletion/archiving of recurrent
tasks by giving the user the option to either continue
or stop the recurrence. The two main use-cases are:

\- You have a recurring task for a weekly meeting.
Next week, the user will be on time off. You are thus deleting the task.
However, you would still like tasks generated for the following meetings
and to keep track of the previous meetings.

\- You have a recurring task for a weekly meeting with an employee
that has just been fired. You are thus deleting the task and
you won't need this recurrence anymore.
(You may or may not want to keep track of the previous meetings.)

The main issue we are currently facing is that we need a task that acts
as a template for the recurrence to continue. This means that a user
cannot delete all of his tasks without breaking their recurrence.

Consequently, we will be using a "task template" for each recurrence,
which will only serve technical purposes and be invisible to the users.
When the recurrence is stopped, the task template is deleted.
This simplifies the technical and functional implementation as the user
won't be able to modify the template themselves.

\- Added task templates to recurrences in the data.
\- Deleted "all tasks" option form recurence update and changed "this
and following tasks" to "this and future tasks". Most of the time, the
user is going to update the most recent task, and it doesn't make
any functional sense to update past ones.
\- Same options for delete and archive.
\- No recurrent subtasks allowed anymore.
\- `date_deadline` is copied. We compute it by adding the delta between
the create date and the `date_deadline` of the template to the next
recurrence date.
\- Added filter to several view not to display task templates.

task-2937565

--
I confirm I have signed the CLA and read the PR guidelines at www.odoo.com/submit-pr

Conversion of the gantt view to OWL.

Along the way the UI has been changed:
- hover a pill does not make a popover appear anymore. It is now
  necessary to click on the pill to make it appear. A button "Edit" in
  the popover still allows to edit the pill (if edition is available).

The unused arch attribute collapse_first_level has been removed.

Technically:
- complete revamp of the DOM and class names to trim down dead code and
  needless nesting;
- the gantt view now makes use of the CSS display "grid" property in
  several places (most importantly in the main row container), further
  simplifying the DOM and allowing for list virtualization;
- this virtualization process ensures that only visible rows (and
  their related elements) are effectively rendered in the DOM. This is
  done using the newly added "useVirtual" hook.

The rendering process of the new gantt view should thus be a lot quicker
as a result.

Enterprise counterpart PR: odoo/enterprise#36202
Task Id: 3105022

Co-authored-by: Bruno Boi <boi@odoo.com>
Co-authored-by: Julien Mougenot <jum@odoo.com>
Co-authored-by: Mathieu Duckerts-Antoine <dam@odoo.com>