Improve service manager URLs

* Make standard URLs the default constructor, since the alternative is for testing, not customization.

* Allow services.config to be any URL, defaulting to a file, so that resources in a .jar can be used, too.

With previous branch (included), this allows a caller to start the SQL layer in a JVM without any external config files. Whether this can actually be done in production from an .ear / .war remains to be seen, but I don't see much harm in the potential.