add paypal and dummy payment modules

Conflicts:

	boilerplate/settings/shop.py
save the modules in the application instance

Conflicts:

	boilerplate/apps/store/apps/checkout/app.py
the first step in checkout is selecting the payment method. Redirect to selected module's index url

Conflicts:

	boilerplate/apps/store/apps/checkout/views.py
missing module name
index url for paypal module
imports cleanup
paypal's "root" url is just redirect to paypal express view (if not using payflow-pro)
maintain PaymentDetailsView and FormView functionality in checkout app
note: remember paypal doesn't require preview
start working on Dummy payment method views
base class for payment modules root view
make modules into a property
namespace urls and provide good default views
adjust dummy module to new base
adapt paypal views to new base
add parent payment module to the view for easy access
Make the BaseView a mixin so other views can use it too
docs
use dummy-specific forms
remove label from PaymentModule choice