improve support for https

proxy to internet:
if surfex-proxy as user agent request is to HTTPS resource, current keystore fails to recognize as trustable, investigate and if possible fix this. Hopefully this will not require adding certs for all visited sites... if that is the case, then investigate how to do that in compliance with chain of trust. Upgrade to latest Java SE and test with that first.

browser to proxy:
generate a new self-signed cert on first start up, regenerate a new one on user-initiated-demand

both:
instructions on how to register cert in local keystore
option for user to configure which runtime keystore to use - Java default, a specific one, or the no-op trust all one