This commit adds user feedback in the form of a message logged on the related
document (mailing.mailing) when testing a mailing/sms.
Before this change, when sending an email to your own mailbox for testing
purpose, or when sending an SMS to your phone, you did not get any interface
feedback on whether it worked or not.
Now, a logged message will show if it's successful and if not, explain why it
failed with a short error message (no IAP credits / misconfigured outgoing mail
server / ...).
In addition, email and phone inputs are now split on the '\n' character instead
of a coma, which allows easier validation of the email addresses.
Task-2375526
closesodoo/odoo#63421
Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>