This removes the `FIRMessaging_FAIL` macro which was using `__builtin_trap()`, and replaced with `NSAssert` calls. These `NSAssert` calls may not get called in release builds, and so we also log them with FIRLogger error messages.
The RMQ database open error result code is now parsed and included in the error message to help us identify causes for #199 .
* Remove mostly unused code from FIRMessagingLogger
This cleans up some left-over old logging logic from before we moved to FIRLogger in Firebase Core. We no longer need this logging functionality.
* Delete FIRMessagingConfig.{h,m}
We no longer need a config class to store an unused log level filter (that filter is no longer needed).
This shows the simple property, shouldEstablishDirectChannel, to open a new channel, and how to show incoming messages with the iOS 10 delegate handler