Disable/hide email button for authors 

who haven't published in the previous six months.

Applies to https://github.com/GigaOM/gigaom/issues/4939
```php
if ( ! isset( $last_post_query->posts[0]->post_date ) )
{
  $last_date = 0;
}
else
{
  $last_date = $last_post_query->posts[0]->post_date;
}