In the chatter, the attachment preview image size is fixed with 160*160
but the actual preview area is 200*200px so the image is not filling correctly.
It appears padding around the image, especially visible when hovering it.

So with this commit, We should make sure to use a properly sized image in the
preview. we have to also provide the perfect resolution and preview for
the small images without upscaling incorrectly. For large images, it should be
display based on the aspect ratio.

Task : 2483885

closes odoo/odoo#68696

Signed-off-by: Sébastien Theys (seb) <seb@odoo.com>

Also make rounded style for composer tool buttons.

task-2282342

closes odoo/odoo#56282

X-original-commit: 307fa6877ad72fe0afb10f1b4e67ec573422b732
Signed-off-by: Alexandre Kühn (aku) <aku@odoo.com>

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>