Only offer to save address if a user is logged in.
Associate CreditCard with users and payment methods

Conflicts:
	core/app/models/spree/credit_card.rb
Remember customer credit cards on checkout

Mostly inspired by Jeff Squires spree_reuse_credit_card extension, see
https://github.com/jsqu99/spree_reuse_credit_card

Once customers enter their cc info and recurring tokens are saved for
those credit cards the store can remember that info and display the
cards back to the customers so they don't have to enter cc info again
Provide interface to list and disable user payment sources

Users might include the Core::UserPaymentSource into their user models
or implement their own methods to deal with payment sources
Add checkout specs for using existing payment sources
Add CHANGELOG entries for reusing credit cards
List customer payment sources on backend new orders

Fixes #4412
Add timestamps fields to spree_assets

Initial motivation here was make assets_spec green. As of Rails 4.0.4
touching an object without timestamps won't touch its associations. Plus
timestamps are usually handy so no reason for not having them in
spree_assets too

See https://github.com/rails/rails/commit/73ba2c14cd7d7dfb2d132b18c47ade995401736f
Use stub_model rathen than mock_model

Make rails 4.0.4 build happy