This commit is a significant rewriting of client-side discuss, chatter,
chat window, and messaging menu using OWL. The behavior should be broadly
the same, with some slight functional changes here and there.

From a technical standpoint, the code of messaging is mainly organized in 2
main groups of modules:

- models, which are logical entities that depict the client-side state of
  messaging as a whole.
- components, which are in charge of displaying information from models.

This refactoring also introduces new JS guidelines regarding folder structure
(/static) and naming rules for JS modules.

Community PR: https://github.com/odoo/odoo/pull/39023
Enterprise PR: https://github.com/odoo/enterprise/pull/6249

Task-1914207

This PR is a collaborative work by Alexandre, Julien, Sébastien and Xavier,
with the precious help of Lucas to speed it up towards the end.

closes odoo/odoo#39023

Related: odoo/enterprise#6249
Signed-off-by: Alexandre Kühn (aku) <aku@odoo.com>
Co-authored-by: Alexandre Kühn <aku@odoo.com>
Co-authored-by: Julien Giannone <jgi@odoo.com>
Co-authored-by: Lucas Perais <lpe@odoo.com>
Co-authored-by: Sébastien Theys <seb@odoo.com>
Co-authored-by: Xavier Dubuc <xdu@odoo.com>

PURPOSE

We are currently working toward turning every user avatar (i.e. the round
picture of the user) in a shortcut to open the chatbox to that user. It only
makes sense to also have the user avatar in the header of the chatbox
(like in Facebook)

SPECIFICATION

Replace the current IM status colored dot of the chatbox header by the same
avatar/im_status compound currently used in the chatter.

LINKS

Closes https://github.com/odoo/odoo/pull/51258
Task-2256061

closes odoo/odoo#51258

Signed-off-by: Alexandre Kühn (aku) <aku@odoo.com>

The customizable "out of office" text was removed from the editable views as
part of task-2053585, but some places in the code were still using it, even
though it was never set anymore.

This commit removes the obsolete code.

Part of task-2171864

closes odoo/odoo#44968

Signed-off-by: Alexandre Kühn (aku) <aku@odoo.com>

This commit adds the out-of-office ribbon at the top of the
conversation in the discuss app.

Task-2066672

closes odoo/odoo#39362

Signed-off-by: Alexandre Kühn (aku) <aku@odoo.com>
Co-authored-by: Mohammed Shekha <msh@odoo.com>

Part of task 1896658

Co-authored-by: Aaron Bohy <aab@odoo.com>
Co-authored-by: Christophe Matthieu <chm@odoo.com>
Co-authored-by: Mathieu Duckerts-Antoine <dam@odoo.com>
Co-authored-by: David Monjoie <dmo@odoo.com>
Co-authored-by: Martin Geubelle <mge@odoo.com>
Co-authored-by: svs-odoo <svs@odoo.com>
Co-authored-by: Vincent Schippefilt <vsc@odoo.com>

When on leave, the im_status can be either leave_online or leave_offline.
This will allow to display a specific icon and a default message when the user
is not at the office.
The leave can have an out of office message. This message will be displayed
in the chat window instead of the user ooo message, and the end date of the leave will be displayed too.

Technical details.
Right now the im_status access leaves directly to know if a user is on leave or not.
An index has been added to optimise this request (thanks to rco).
A solution to optimise this would be to compute part of the information in a cron.

Task: 1856205

This commit adds the seen icon next to a message for all channels
except livechat.

It tracks received and seen messages for all members of the channel.
Icon is either 1 or 2 check(s) ('v' or 'vv').

Those are the different states of this 'seen' icon:

  ICON:                           DESCRIPTION:

  no check .................. no one has received the message.
  1 check ................... some members have received the
                              message, no one has seen it.
  2 checks (greyed-out) ..... some members have seen the message,
                              some or everyone has received it
  2 checks (green) .......... all members have seen the message

This icon is not shown for messages preceding the last message seen
by everyone, in order to reduce visual noise.

Task-ID 1881001

Before this commit, we had the following issue:

1. Open two tabs A & B.
2. Receive a message from a channel in tab A.
3. Mark it as read in tab A by clicking on the
   chat window of the channel.

> The unread counter is correct in tab A: no
  unread messages on this channel, and the
  messaging menu counter has been updated.
> The unread counter is not correct in tab B:
  it still has unread messages on this channel,
  and the messaging menu counter has not been
  updated.

The issue was caused by not notifying the updated
unread counter to the widgets when receiving the
'channel_seen' notification from the longpoll.
It was working in tab A because this is were we made
the action, so that it already marked messages as
read without waiting for the longpoll response.
However, Tab B has to wait for the longpoll response
to update the unread counter. It was updating the
counter, but it was not notifying the widgets.

This commit fixes the issue by letting the widgets
know when the unread counter has been reset.

Task-ID 1911239

closes odoo/odoo#28833

1. Removed `getLocalMessages` method in mailbox, and replaced
   with an override on `getMessages`.

   (This method was used before the distinction was made
   between `getMessages` and `fetchMessages`)

2. Removed unused method `_warnUpdatedUnreadCounter` in
   abstract thread window.

   (Leftover from an early POC)

3. Set the default value `''` for the status of a thread.

   (The method `getStatus` should always return a string)

4. Enforce default value `false` for detached status of channel.

   (The method `isDetached` should always return a boolean)

5. Improve readability of some tests.

   (removed useless variables and/or redundant code)