Email delivery record improvement

[Nness]

• [x] Record which delivery method been used
• [x] Record which template used for this email delivery.
• [x] Record which event for this email delivery. (approval required? mail token?)
• [x] Record ticket related info, if email delivery related to ticket.
  • [x] Ticket ID
  • [x] Ticket Identifier
  • [x] Ticket summary
• [x] Add match in index for To email
• [x] Add full text search in index for subject
• [x] Filter by delivery method (use new multi delivery system)
• [x] Index for ticket ID.
• [x] Index for ticket identifier
• [x] Index for email event.