Add email_report_recipients and email_report_prefix options.

Email reports allow system administrators to be notified via email
when a registration-related activity occurs.  If the email_report_prefix
option is specified, the email subject line is prepended with its value.
Merge pull request #86 from akirisolutions/feature/email_report_recipient

Add email_report_recipients and email_report_prefix options.

Thank you!