Add POS terminal category visibility system

Add posterminal and posterminalcategory tables to control which categories
are visible on each POS terminal. The existence of a row in
posterminalcategory means the category is visible on that terminal.

Store methods:
- posterminal.list/upsert/delete - CRUD for terminals
- posterminal.setOn/setOff - toggle single category on a terminal
- posterminal.setOnAll/setOffAll - toggle all categories on a terminal
- posterminal.getCategoryPosterminalIds - internal, used by category tree

The category tree (getTreeForCompany) now includes a posterminalIds array
on each node listing which terminals have that category enabled.

src/sql/purge.js

@@ -3,6 +3,8 @@ export const TABLES = [
   'companyuser',
   'syncpos',
   'companysetting',
+  'posterminalcategory',
+  'posterminal',
   'numbers',
   'manifestarticle',
   'manifest',