Allow sites to not have Billing Address Location Type

Overview

Currently CiviCRM has a confusing array of default location types and flags. This issue proposes changes that would allow the Is Billing flag to be the only indication that a location is the billing location rather than also having a Location Type of Billing. The intent is to allow instances to experiment with simpler approaches to Location Types in order to improve the usability of the product.

Example use-case Add a hook to allow billing location to be determined by an alternative implementation. Sample LExIM extension approach would return the address which has isBilling==True if there is no LocationType of 'Billing' or if there is no address passed to function with LocationType of 'Billing' from https://github.com/civicrm/civicrm-core/blob/master/CRM/Core/Payment/BaseIPN.php#L491

In current places where code creates a 'Billing' type address one potential approach would assume it should be home location type for individual and household contacts and work for organizational contacts. In all cases the Is Billing would still be set. The objective of this proposal is to refactor and introduce hooks in order to allow a LExIM extension to work. More details about specific places in code that need to be changed and ideas on what exactly to do in a simpler approach to be provided if there is potential for this proposal to go forward.

Comments

Just testing water for potential support before developing more detailed proposal. Otherwise we'll likely just override core for this particular client.