Fix sending test emails.
Fix sending messages with empty subject when subscriber does not have any properties.
Fix receive worker.
Add name to emails.
Show email statistics on sender statistics page.
Calculate maxSubscribers with the locales of the email variations.
Send email messages in random() order.

It will allow multiple send workers to operate together.
Remove unnecessary error messages from admin.
Fix save email variation message on admin.
Fix a typo on sender page of admin.