@ashfurrow => Registration Flow

This takes someone new to Artsy to being registered and full set up. It also deals with logging in via Artsy u:p and updating the user to be registered and then presents you paddle + pin.

Attached to it is an experiemental version of web based bidding. There's complications around access tokens when using pin + number which basically makes it more effort than it's worth now. So I'll be switching it out in the next PR with the original native version and just going with that. Think I've got enough time to make all of it's required states.

*Note:* @1aurabrown this will not compile on yours anymore because you'll need to add some more CocoaPods keys. Run these

```
bundle exec pod keys set CardflightMerchantAccountStagingToken XXXX
bundle exec pod keys set CardflightMerchantAccountToken YYYY
```
This block could be structured a little more explicitly. Right now if reminds me of nested callbacks using ordinary blocks. I think something like this might be better, but it's up to you. 

```swift
XAppRequest(endpoint, method: .POST).filterSuccessfulStatusCodes().mapJSON().doNext({ [weak self] (json) -> Void in
    if let nav = self?.fulfilmentNav() {
        if let token = json["trust_token"] as? String {
            nav.trustToken = token
            nav.xAccessToken = token
        }
    }
}).then {
    if (/* check if trustToken is set*/) {
        return nav.updateUserCredentials()
    } else {
        return RACSignal.empty()
    }
}. subscribeNext({
    self?.performSegue(.PINConfirmed)
    return
}, error: {
    println("error, the pin is likely wrong")
    return
})
```