Handle reply to document
Cleanup unused variable
Add oe_display_only as inverse of class oe_edit_only

See https://www.odoo.com/forum/help-1/question/inverse-of-css-class-oe-edit-only-11853
Fix some french translations
Strip In-Reply-To header

Header could be expressed like this:

In-Reply-To:
	<4ba8f246904b4fedb49fbab7945a7f82@AM3PR06MB433.eurprd06.prod.outl$$k.com>

The message lookup fails if header is not stripped