Mod11

## API Wrappers
- `StripeWrapper` module for Stripe credit card processing
- Refactor UsersController#create to utilize `StripeWrapper`

## Testing
- `user_sign_up_spec` feature spec
- `vcr` cassettes for optimizing tests with external requests
- `stripe_wrapper_spec`
- Stubs to eliminate redundant testing of `StripeWrapper` in controllers
- `selenium-webdriver` and `capybara-webkit` gems for js testing