Stripe api wrapper

This contains the following features:
* implements the StripeWrapper for wrapping the Stripe credit card processing API
* addition of vcr gem and gems used in rspec support for javascript testing
* user invitation feature tests updated to take into account the credit card processing
* new feature tests for the non-invited user registration process
* new "BuildInfo" model which is meant to contain build date/timestamp and machine and user info of the build environment prior to deployment