Configure official document templates for an organizational party

For an organizational party, add possibility to give the specific template to use for official document like invoice and order.

The first step is adding mechanism to indicate what template to use for a party, for that :

• add CustomScreen entity (like CustomMethod) to prepare and organize your screen by theme
• add PartyPrefDocTypeTpl as association entity between an organizational party, a document type and a custom screen

For use case, I create a new invoice template for oriented on EU format (in process) with VAT directly display on invoice item.

Related mailing list thread : https://lists.apache.org/thread.html/4a5244e6d022564414e4f4a5676f72288d4000913ec2afa7e4af5e1a@%3Cdev.ofbiz.apache.org%3E