Config file overhaul

* Change config file language to YAML from JSON
* Use nconf module for handling configs
* Added schema validation for the config file
* Enable config overrides from command line and environment variables
* Allow setting config file from command line
* Altered tests to use their own dedicated config file in test/config.yaml
* Pregenerated a set of PKI keys and certificates in test/ssl/ whic the
  test config points to. These are shared with svmp-server.