added populate list and attrs to repo classes
fixed dataflow in sales_engine and database
removed unnecccary ref to sales_engine in db.rb
implemented all method on repos
implemented random method on repos
added find by id, find by invoice id, and find all by invoice id for invoice item repo
added findallbyid to inv item repo
added find and find all by item id to iir
added find and findall by quantity to iir
added find methods for unit price on iir
added find by methods for created at in iir
added find by updated at methods to iir
added all find methods to customer repo
repeated findby pattern on invoice repo
repeated findby methods for items
findby methods for merchant done
findby methods now complete for all classes