@ashfurrow => support entering emails in bid fulfillment

* Moved the SaleArtwork into the BidDetails object, so that it can be accessed from any VC. 
* Changed "confirm"-y buttons to have a lighter text on the disabled state so I could tell when it was enabled / disabled
* Added a regex checker for the email address
Probably not a huge deal since `testPredicate` should never be nil, but this *could* return either a `Bool` or `nil`, which is kinda problematic if you're assigning to a Swift property (assigning to the `confirmButton`'s `enabled` property is fine). More explicit could be:

```swift
if let result = testPredicate?.evaluateWithObject(text) {
    return result == false
} else {
    return false
}
```