PayPal SDK Integration

- Adds paypal SDK libs
- Adds PayPal credentials to manifest
- Adds PayPal environment setting ("sandbox")
- Adds Camera Permissions for PayPal card scanning
- Adds Camera features for PayPal card scanning
- Defines services and activites for PayPal and CardIO
- Adds PendingPaymentActivity and tests PayPal integration
- Updates the Request class to expose its bid value in PayPal-friendly getters
- Updates Helpers to add a vendor in the mock Request