FUIArray sample in Swift

[jayvenn]

Request

[morganchen12]

There's limited information in the FirebaseUI Database readme. We probably won't add more until the functionality of FUIArray is extended, as it's currently mostly an implementation detail of the data sources. #186 extends FUIArray to be more interesting, after which some samples would be good.

I'm going to close this issue though, as your wording isn't very specific.