Defer payment provider logout (bug 1037513)

The API to start a transaction doesn't return
a payment provider because the transaction has not
been created yet. This defers payment provider logout
until right before we redirect to the provider's web
flow.
Merge pull request #89 from kumar303/defer-logout

Defer payment provider logout (bug 1037513)
Add Universal Analytics (bug 1018934)
Fixes following testing with Chrome GA debugger