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.
TL;DR: In retrospect, I probably shouldn't have even mentioned the RFC and
simply said, "because 'From' is what nearly every email client says".

> ... *it's short/simple*

> ... *it's the term most likely to match what users are accustomed to seeing
in their respective email clients*.

My rationale wasn't that end-users would prefer "From" because of the
specification, but rather because of convention.

Because of its inclusion in the specification, _every_ email client has
a concept of "From", as its one of the defining characteristics of an
email message, being one of the few required fields. Consequently, email
client developers have mirrored this language in their user interfaces.
Every [0] email [1] client [2] I [3] use [4] tells me "From" whom a message was
sent, not by whom it was "Sent" nor who was the "Author".

From this perspective, _any_ term beyond "From" is a departure from
convention.

Either way, I won't lose sleep, so I defer to UX.

[0] ![0](http://9to5mac.files.wordpress.com/2014/01/addaline.png)
[1] ![1](http://g04.com/images/gmail/gmail_filter.jpg)
[2] ![2](http://untetheredoffice.com/wp-content/uploads/2010/07/Email-Filters-and-Folders-thunderbird-filters-e1279183740393.png)
[3] ![3](http://www.uxmatters.com/mt/archives/2009/07/images/figure_5_hotmail.png)
[4] ![4](http://help.yahoo.com/cpp/images/cg3/cg_addfilt1_yp_1.gif)