Several invoice issues adressed plus more

Invoice now contains a reference i.e. reference number.
Invoice now is shown with actual price, from previous 0.
Ad and its subclasses now generate their own descriptions.
Sale now can calculate its total price.
Sales ad list now is properly fetched from db.
Ads can now be generated directly from sales site.
Several xml files now have updated their licences.
Tomcat plugin now added on final build.