[MERGE] portal, website_{mail, rating}: fix frontend rating and reorganize portal chatter overrides

PURPOSE

Fix frontend rating and clean a bit module organization.

SPECIFICATIONS

Fix rating in frontend (website_slides, website_sale): rating is halved at each
update and new entries have no rating.

Also reorganize portal chatter overrides

* rename files to ease code reading and discovering;
* move assets in their own file to better understand modules;
* move rating widget in its own file;

LINKS

Task 2057301
PR #35870

Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>