Improve insight email subject lines

Set the subject line to a high or medium emphasis insight headline,
converted to second person.
New insight: Gender breakdown of Facebook comments/likes
Gender analysis tweaks

* Don’t count posts by yourself, or multiple comments by one person in
the gender total
* Do specify network in the DAO calls
* Add a headline case for when your response is 100% male or female
* Add tests
Gender Analysis insight: test on staging