Initial Kerplapp SSL repo support.

Lots of work left to be done. Presently generates a new KeyStore with a self
signed cert for each installation. Hardcoded passphrase. All very nasty and
initial, but it works!  Requires patched NanoHTTPD.

refs #2541
Switch to HTTPS / fdroidrepos in URLs.

Use https:// for all normal URLs, and fdroidrepos:// now that the repo is being
hosted w/ SSL.
Use gen time for HTTPS certificate serial.

Firefox complains when it encounters two SSL certificates with the same serial
(as happened when you reran Kerplapp and got two different certificates with
a serial of '1').

Until better self signed certificate generation is in place let's use the
current time as the serial.