Refactor URL display on `status-buffer`

[aadcg]

Now that #3473 has been solved, it is the right moment to improve the UI.

In the case of HTTP(S) URLS:

• Omit the URL's path, query and fragment in the status buffer à la Safari (still available via set-url);
• Indicate whether it is encrypted (think https://github.com/marcinkosztolowicz/nx-secure-connection-indicator but with a better UI).

For other schemes, the URL should be fully shown.

I have a mental picture of how it should look, but it's wiser for @jmercouris to start on a blank page.

http://httpforever.com/ is helpful to test on HTTP.

[jmercouris]

Yes! :-)