Making RECAP advertise itself

This release makes it so a small list of websites can detect if RECAP is installed. Currently that list includes only one website, CourtListener.com, and adding more will require an update to our privacy policy (which we'll advertise). CourtListener.com is run by Free Law Project, the makers of RECAP.

Letting CourtListener.com know if RECAP is installed will let us encourage more people to install RECAP. The thought is: If you're using the RECAP Archive on CourtListener.com, you should probably be using RECAP to contribute documents you purchase.

No other changes in this release.