Integrated changes for OVPMS-1517 Add a new Discount type to produce a discount based on cost price plus a rate, contributed by Ben Charlton

git-svn-id: svn://svn.openvpms.org/openvpms/archetypes/trunk@6195 9e4fa352-aafb-0310-9071-df624684024b
Added CustomerTaxRules.getTaxRate(Product product, Party customer)

git-svn-id: svn://svn.openvpms.org/openvpms/archetypes/trunk@6197 9e4fa352-aafb-0310-9071-df624684024b