Add "Address.isDefault" boolean <-> "default"

Add support to get collection with handle

Remove reference to private class.

Add customer update endpoint

remove customer update unit test

Introduce BUYCustomerToken and update APIs

Use the customerID from the customerToken instead.

The customerID is available from the `BUYClient.customerToken` property, which must be set before using these methods.

Remove Swift Sample App

Product tags support

Use NSNumber for product id in Client APIs

Remove password confirmation

Fix Swift Sample App

Fix type for defaultAddress on Customer