@1aurabrown => Place Bids

Adds the networking required to send the POST to submit a bid. Then sits at the confirmation page. Removes the `BiddingWebViewController.swift` 

Also:
* fixes #145 
* fixes #137 
* partial fix for #144
also are you sure this logic works? I think you can remove `?? RACSignal.empty()` because the first half will never be nil. You're already returning an empty signal from `setBidderIfNeeded` if the bidder has already been set