Checks don't handle EML references

[gothub]

The quality checks currently use XPaths to extract information to validate from documents. EML can use a <references> subelement to refer to content elsewhere in the document. For example:

    ...
    <creator id="id001">
      <individualName>
        <givenName>Michael</givenName>
        <surName>DeGrandpre</surName>
      </individualName>
      <organizationName>University of Montana</organizationName>
     ...
    </creator>
    ...
    <contact>
      <references>id001</references>
    </contact>
    ...

Develop a strategy to handle these references, and which checks need to follow them.