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?~~ Following discussion currently it's not so following that lead.
 * ~~If errors are thrown in the API do they need to be handled on the client? I've left this out currently.~~ Agreed to log errors and not show one for the first cut.

Should go without saying, but DO NOT MERGE as this will need to be landed after the tag.