Stripe wrapper

1) add stripe_wrapper.rb and spec
2) add travis ci and set up
3) add stubs and mocks to users controller and add/change more specs
4) add VCR and webmock
5) add selenium-webdriver and js: true
6) add capybara-webkit driver to use instead of selenium in some cases
7) add user registers feature spec
8) add stripe initializer
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