By default use preferred device sample rate instead of 44100 in RtAudio driver

Instead of defaulting the sample rate to 44100, use one of the supported device sample rates as reported by RtAudio (see https://github.com/samplecount/methcla/blob/develop/platform/rtaudio/Methcla/Audio/IO/RtAudioDriver.cpp#L71).

Use the same sample rate for input and output device and throw an exception, when no suitable sample rate can be found.
