Improved product average shelf life calculation (references #2283)

migrations/0222.sql

@@ -0,0 +1,14 @@
+CREATE INDEX ix_stock_log_performance1 on stock_log (
+	stock_id,
+	transaction_type,
+	amount
+);
+
+CREATE INDEX ix_stock_log_performance2 on stock_log (
+	product_id,
+	best_before_date,
+	purchased_date,
+	transaction_type,
+	stock_id,
+	undone
+);