To mardini a set assess priority

Deferring to Gabe and Pink. 

Let's get regular link peek&pop implemented first and then we can assess how best to prioritize application throughout our app. I think this is a good idea. 

Note that Peek and Pop is still not a done deal. 

See: https://bugs.chromium.org/p/chromium/issues/detail?id=897261#c33
and 
https://bugs.chromium.org/p/chromium/issues/detail?id=643318#c21

I created rdar://46356051 for WKWebView peek/pop, which Pink escalated with Apple.  It seems that they're interested in fixing this for us, so hopefully the WKWebView implementation can be fixed with the next iOS version when WebKit supports what we need.

FWIW, we could implement 3D touch to open links from the NTP, since we don't need to worry about restoring session history like for arbitrary WKWebView links.  That being said, I don't know from a product perspective if it's desirable to support link previews from NTP before we can support them elsewhere in the app.

Let's wait until Apple (hopefullY) allows us to support peek and pop throughout the app. Offering it only on NTP may be more frustrating than helpful to users, since they won't necessarily realize the pattern of when it works and when it doesn't