there is no reason why we want to store the bytes of the base64
encoded string. Simply store the string itself.
Also add a convenience method to get the decoded bytes of the PubKey.
- Reduce the amount of types that are subtypes of NamedElement. See
javadoc of NamedElement for rationale.
- Work more with XmlEnvironment in XmlStringBuilder.
- Some minor changes to XmlStringBuilder API.