refactored checkout controller and fixed issues in it
fix exception due to mass assignment of amount and create unique transaction_id
add specs for the checkout controller, refactored paga_notification and transaction
fix error when payment failed, plus add transaction_id to transaction, modify specs for the same
remove after_update_attributes method which is now removed from spree stable 2-0 version
fix when 2 payment methods are present
add rspec and ffaker, sqlite dependency back in gemspec