Initial XCTest async testing.  Comment out lines 19 through 21 in AppDelegate if running Tests to avoid the app initializing Hermes instead of the tests.
Introduced a high level model and entry point for client code into Hermes land, that abstracts away all CPP objects.
Initial implementation of a Reactive Signal to convert CPP callbacks into Objective-C block processing.  Client code only sees Objective-C.
CocoaLumberjack logger added to Podfile and .pch file though not yet used (needs team decision).