Make Transcoder and Converter pluggable

While the current structure of the SDK supports the ability to provide custom implementations of the transcoder, there is no place to inject a custom transcoder. This ticket is to make the Transcoder pluggable:

-The ClientConfiguration should provide a factory method/property for assigning and creating transcoders. Something like: Func<ITranscoder> TranscoderFactory

. for example, look at ClientConfiguration.Timer.

• The current transcoder (DefaultTranscoder) should be the default; to override you assign a new Func to the TranscoderFactory

-The SDK should create the transcoder from the Func, not via "new" - like it currently does.

-From a consumer perspective, there should be no impact - 100% backwards compatible without having to modify existing application code.