Call configure_transaction from client-side WiP (bug 987824)

Following a discussion with @kumar303 instead of making an interstitial page, there's now a new url that is called from the client-side that starts the transaction instead of from within the lobby view.

Remaining questions  I have:
 * This has the same setup in as the lobby view. Presumably there's not any need to do anything with the verified_user decorator is there?
 * If errors are thrown in the API do they need to be handled on the client? I've left this out currently.

Should go without saying, but DO NOT MERGE as this will need to be landed after the tag.