[FIX] web, website: overrideable images controller

The `binay_image` and `content_disposition` are moved
from the web controller to the `ir.http` model,
to be able to override these methods.

This makes possible to browse the records images as sudo
when the record is published on the website.
e.g. to see the partner images on the website `/partners` page
from the `website_crm_partner_assign` module.

opw-659244