payment: email sender should be tickets@jprime.io, not conference@jprime.io

[mihailstoynov]

Fix the sender, the password for the email is the same.

[ivannov]

You remember, we tried it with sending session proposal confirmations from cfp@jprime.io. But it turned out that Spring Mail / Spring Boot integration supports just one property in the application properties for email user name (and respectively one for its password). Not sure how it can be fixed.