provide a resultType combo box when editing XPath expressions so we can specify things like String return types

 <camelContext trace="false" xmlns="http://camel.apache.org/schema/spring" xmlns:foo="http://example.com/bar">
    <route>
        <from uri="direct:MyEndpoint"/>
        <log message="Input Message ${body}"/>
        <setHeader headerName="rid">
            <xpath resultType="java.lang.String">/foo:Request/@requestid</xpath>
        </setHeader>
...
    </route>
  </camelContext>