refitting methods for all files
Fixed Customer and Merchant Repos, tests and classes
Fixed methods for invoice_items and invoices and corresponding tests. Rake test passes. Items and Transactions still to do
Refactored the each/collect methods to one line, and finished refactoring the methods for all item and transaction files. Rake test passes
Began connecting merchants, items, invoices and invoice items by calling other classes through specific object information
Finishes connecting relationships as required in the Sales Engine spec. Needs fixes for tests.