[stripe] addd stripe js payment factory and services.
[stripe] add docs.
[stripe] add checkout factory.
[stripe] add stripe keywords to composer.json
[stripe] add example of stripe checkout.
[stripe] add obtain token and create charte actions.
[twig] use helper method from twig factory to guess views path.
[twig] workaround the bug in twig bundle.
[stripe] add tests for payment factories.
Merge pull request #144 from formapro-forks/stripe-integration

[stripe] addd stripe js payment factory and services.