adds Venmo API to transactions
completes transaction for loan repayment over Venmo
adds field to package.json to configure stub for Venmo transaction (for testing without making actual transactions)
stubs out venmo in package.json, adds db connection loss event listener to return 503
Merge pull request #95 from caasjj/integration

Adds option to stub out Venmo in package.json, listens for database connection loss and returns 503 - service not available