feat: Item validate cost, income and inventory account type.

feat: Style sales and purchases forms - 80% progress.
feat: Validate purchase-able and sell-able items in invoices and bills.
feat: Fix bugs in inventory FIFO/LIFO cost methods.

client/src/components/classes.js

@@ -0,0 +1,4 @@
+
+export default {
+  DATATABLE_EDITOR: 'datatable-editor',
+};