Disable/hide email button for authors 

who haven't published in the previous six months.

Applies to https://github.com/GigaOM/gigaom/issues/4939
`strtotime( '-3 days' ) > strtotime( $last_post['date_checked'] )`

Why so much `strtotime()`? If the data is saved as a unix time stamp, we can compare against `time() - 933120000`