Update inventory change tracking/reporting to handle inventory_unit changes

[jmcameron]

Currently, the inventory change tracking and reporting does not seem to track changes to inventory_units and inventory_group. There are a few spots in the code where it appears that was started, but this functionality should be improved so that the Inventory Changes Reports will also list changes in inventory_unit and inventory_group. The latter is particularly important to track changes in account numbers for inventory groups.