Self-signed cert

[michielbdejong]

Building on #13, switch from http to https.

• Add code that generates the self-signed cert and saves it on the file system on first boot.
• Switch https://github.com/fxbox/foxbox/blob/master/src/http_server.rs to https, using that cert.
• Update the hyperlink to the basic web app to its https-hosted URL.
• Add/update tests.
• Update the user manual to say 'https://foxbox.local/' instead of 'http://foxbox.local/' and add part about adding an exception to accept its self-signed cert.

After I get that working, I'll look at improving it further, e.g. avoid bad UX of adding the exception for the self-signed cert, and not requiring the connection to the router to be via ethernet.

[michielbdejong]

Developing in https://github.com/michielbdejong/foxbox/tree/https-self-signed

[michielbdejong]

Step 1: Create cordova plugin add https-tofu based on TrustManager class.
Step 2: Beyond TOFU - add support for specifying/checking either the cert to pin itself, or its fingerprint

[samgiles]

I'm working on some of this right now in https://github.com/samgiles/foxbox/tree/https-support - mainly updating the server to use https, part 2 here.

[michielbdejong]

Done in #77.