"Your privacy" section requires measurements

[devinreams]

A quick discussion with legal, product, and Test Pilot engineering has led me to think a nice improvement would be for us to "make it possible to leave off the bullets sections" in the "Your privacy" section.

There are cases where the "measurements" in an experiment can't fully capture everything we want to say, and the privacy_notice_url and a blurb should be sufficient to let users know where to get more information.

A rough proposal would be to:

• make sure the page doesn't crash if measurements is missing from experiment yaml
• check if measurements is empty and if privacy_notice_url is not, then modify the blurb and still link to the privacy URL

  In addition to the data collected by all Test Pilot experiments, you can learn more about the data collection for {experiment} here.

• make sure the "featured experiment" links and home page modal render properly
  

...or something like that.