Purpose of this commit is to have some demo data that are coherent. Main things
done in this commit are
* clean the body of the first mass mailing given to the user in order to have
a content more inlined with odoo emails;
* update filter of the demo mass mailing to limit the results to something
predictable, aka contacts of ReadyMat;
* update statistics to be really linked to customer of the demo company by
setting model and res_id;
* create a statistics for each child of the company ReadyMat so that stat
buttons redirect correctly to a filetered view;
This commit is linked to task ID 1885121 and closes PR #27003.
Thibault Delavallée
e7c53bd150