This adds support for using any of the following date/time classes:
 - java.util.Date
 - java.time.Instant
 - java.time.LocalDate
 - java.time.ZonedDateTime
 - java.time.OffsetDateTime

With this all usage of Jackson `ObjectMapper` and `XStream` instances
goes through the single utility method in `JsonUtils` or `XStreamUtils`
in order to register default serializers/deserializers/converters.