Schema and backend improvements for Physical Inventory

There appears to be some incomplete and confusing parts to stock management in the schema and in the backend Java code. Notably:

• physical_inventory_line_item_reasons is not actually a table of reasons (that is stock_card_line_item_reasons), but is actually a table of adjustments to a physical inventory line item. Therefore, a better name would be physical_inventory_line_item_adjustments. The Java code has the name StockAdjustment, which would be better named PhysicalInventoryLineItemAdjustment.

• physical_inventory_line_item_reasons should have id as primary key

• physical_inventory_line_item_reasons should have foreign keys for all attributes that make sense (reasonid, physicalinventorylineitemid, stockcardlineitemid, stockeventlineitemid)

• The quantity field for StockAdjustment is a bit confusing, since there is a quantity field in the PhysicalInventoryLineItem; it would be better named something like quantityOfDifference or adjustmentQuantity (in both the backend code and schema); if the class is better named, I might be open to leaving this, as long as it's clear the quantity is the quantity of adjustment, not the quantity of the line item

Acceptance Criteria

• Make schema and code changes recommended above

• Make sure there are no regressions with these changes