CR-7098 OPENDJ-2009 Result codes in logs should be explained

This patch adds LDAP result code appendices
to the LDAP SDK dev guide and to the server reference.

The implementation is quite closely coupled to
the code in org.forgerock.opendj.ldap.ResultCode,
and because it uses Javadoc comment text
it does not provide for generating a localized version.

This patch also introduces a new opendj-doc-maven-plugin
dependency on QDox, which has an Apache 2 license.