PURPOSE
Do like Mail Speakers, but with SMS, in a single "Contact" button.
SPECIFICATIONS
Specifications:
* on event form view, rename "Mail Speakers" button to "Contact Speakers"
and open a mixed for view on mailing.mailing allowing to choose the type
of mailing;
* send SMS to all speakers;
* see https://drive.google.com/file/d/1-7iDaNJSZbdTW1PYMU2vWtfPHGJmN7SF/edit
FP "Testing Weekend nothing works" request
LINKS
Task ID 2075183 (sms on speakers)
PR #37185
