Finally add support of CIDs in incoming emails. Inline images are recognized
and added as attachments. Image links are updated from src=cid: to src=link
using the /web/image controller.
It has been decided to keep the image in atttachments instead of putting them
in base64, like proposed in various PRs. Indeed we prefer to store this data
into the attachments instead of directly putting it in the mail_message table.
Moreover this enable the display of attachments in the chatter and record views.
Thibault Delavallée
f4481ff74e