feature: inform user browser doesn't support secure subdomain on attempt to access

[nick1udwig]

Is your feature request related to a problem? Please describe.
Safari does not work with secure subdomains on localhost.

Describe the solution you'd like
It would be nice if we could inform users that their browser does not support secure subdomains when they attempt to use it. Logic looks vaguely like:

1. HTTP server gets http request to open an endpoint
2. HTTP server sees it is a secure subdomain'd endpoint
3. HTTP server checks headers & URL of request
4. If URL is localhost && headers indicate request is from Safari, instead of redirecting to SSD, print some error informing user something like "Your application foo:bar:baz.os secures your connection using secure subdomains (explanatory link). However, secure subdomains don't work properly on locally-hosted nodes running Safari! Please use another browser"

Notes
Low priority