Enable Freshly Pressed for Jetpack Blogs

Enhanced Distribution: Add a server-side catch that will return JSON
data if ?get_freshly_pressed_data=true
-- will return the WPCOM Blog ID and Post ID (both of which are
probably accessible on the page already, but
this simplifies things and confirms that the Enhanced Distribution
module is enabled (as we wouldn't want to
Freshly Pressed a post otherwise).