Gracefully handle uninitialized Launch Darkly and failed initialization #62

In order to decouple A/B tested components from <LaunchDarkly> initialization, it would be great to have <FeatureFlag> gracefully handle uninitialized LD. (It would log a warning, of course.)

Similarly, if <LaunchDarkly> does not initialize correctly (e.g., with a connection error or account error), it makes sense to log a warning and not crash the application.