Improve message for error creating Name for namespace

If a CND file does not contain a namespace definition, we currently generate an error (upon startup) that is ambiguous; something akin to "Caused by: org.modeshape.graph.property.ValueFormatException: Error converting String to a Name: lt:description".

We should enhance this error message (or provide another more specific one if we can) to suggest checking the CND files for proper namespace definitions.