V6.2: Add error/warning/notice/message functions to display messages to the user

Makefile

images/plg_vmshipping_rules_shipping_messages.png

images/plg_vmshipping_rules_shipping_plugins_icon.png

library/rules_shipping_framework.php

releases/plg_opentools_vm_rules_shipping_advanced_v6.2.zip

releases/plg_opentools_vm_rules_shipping_v6.2.zip

rules_shipping.xml

rules_shipping_advanced.xml

rules_shipping_framework_joomla.php