Update composer.json & dependencies of the project
Merge pull request #870 from stloyd/feature/composer_deps

Update composer.json & dependencies of the project
Move purchase step from PayumBundle into CoreBundle
Merge pull request #949 from stloyd/feature/move_step

Move purchase step from PayumBundle into CoreBundle
Return to payment step if payment failed.
Add translation message.
Add event.
Implemented PurchaseListener