Add check for HSTS preload list

[blackthorne]

As you know, this is a list shared by multiple browsers for websites that should be reached through HTTPS only. This is even more secure than HSTS since it's not prone to MitM on the first request. My suggestion is that you check for the presence of the domain within the HSTS preload list. You can get it at:
https://chromium.googlesource.com/chromium/src/net/+/master/http/transport_security_state_static.json