Created by: josephearl
Add taskForCompletionOfAllTaskResults to match Task.whenAllResult in Bolts-Android. All tasks should be of the same type.
Also add isFaulted property for consistency with Android and C#, tests for taskForCompletionOfAllTaskResults & missing tests for immediate completion of taskForCompletionOfAllTask and taskForCompletionOfAllTaskResults.
Similar to #74 but this adds a new method rather than modifying the existing one.