[mail] allow to specify SMTP's MAIL FROM address to config.sendmails(). Closes #3373620 Also modify testlib.Email so we don't loose this information and may test it.

+
−usr/bin/cubicweb-ctl usr/bin/
+
−usr/lib/PY_VERSION/*-packages/cubicweb/cwctl.py
+
−../cubicweb-ctl.bash_completion etc/bash_completion.d/cubicweb-ctl