CASC-231 HttpsURLConnectonFactory is Not Serializable

Problem: THe HttpsURLConnectionFactory is not serializable, causing problems for clients that must serialize
the principal (which depends on a ProxyRetriever).

Solution: Make the HttpsURLConnectionFactory serializable.

QA Notes: added unit test to confirm serialize-deserialize
I'm always suspicious about ```serialVersionUID``` as ```1L```: why not using a generated value?