OpenVAS v6 and v7 store information in different places of the <result> XML

This commit creates a hierarchy of clases that are able to locate the
information for both v6 and v7. The FieldProcessor of this add-on will
detect the type of report we're parsing and instantiate the correct
version.
Add sample v7 XML
Complete :result template with raw :description field
Thorfile - remove references to Acunetix (c&p error)
Importer - implement XML parsing code