Email content history fix and additions

This addresses a bug in the email content history table where
"Unknown" was displayed in the number of emails sent column if any sort of
failure occurred during email sending. This behavior has been edited so now
the number of emails that failed to send is displayed, along with the number
of emails that were successfully sent. If the email task is still pending,
"0 sent" is displayed.

As a small addition, the table now also includes the authors of previously
sent emails, and the modal window for an email also displays its author.
I recommend using "From", as its short/simple and also corresponds to
RFC822 header semantics [0].

Not only is it the more correct term from a technological perspective,
it's the term most likely to match what users are accustomed to seeing
in their respective email clients.

"Originator Fields" [1]
>  The "From:" field specifies the author(s) of the message,
   that is, the mailbox(es) of the person(s) or system(s) responsible
   for the writing of the message.  The "Sender:" field specifies the
   mailbox of the agent responsible for the actual transmission of the
   message.  For example, if a secretary were to send a message for
   another person, the mailbox of the secretary would appear in the
   "Sender:" field and the mailbox of the actual author would appear in
   the "From:" field.

[0] http://tools.ietf.org/html/rfc822
[1] http://tools.ietf.org/html/rfc5322#section-3.6.2