Merged ReferencingIdentifier with Identifier. This reflect a change in ISO standards,
where MD_Identifier and RS_Identifier (from ISO 19115:2003) have been merged in the
MD_Identifier type in ISO 19115:2014. Concequently all usages of ServiceIdentifier in
Apache SIS have been replaced by usage of the Identifier parent type.


git-svn-id: https://svn.apache.org/repos/asf/sis/branches/JDK8@1629469 13f79535-47bb-0310-9956-ffa450edef68