Cleaned up Shipping Prodiver base code.
Merge remote-tracking branch 'merchello/1.3.0' into 1.3.0
Merge remote-tracking branch 'merchello/1.3.0' into 1.3.0
Extends InvoiceApiController to include GetByCustomerKey.

Added InvoicesByCustomer to MerchelloHelper for customer account pages.
Adds CustomerMemberTypes to MerchelloConfiguration.

Usage: MerchelloConfiguration.Current.CustomerMemberTypes -> returns IEnumerable<string>
Adds Customer configuration element to Merchello.config and a unit test.
Housekeeping
Code clean up
Merge pull request #737 from rustyswayne/1.3.0

Added member types for persisted customers to Merchello.config.  Added invoices by customer functionality.