Channel mapping

This PR supersedes https://github.com/teragonaudio/MrsWatson/pull/165

This introduces input and output buffers for each plugin. It also fixes speaker arrangement. It also reduces code (removes the bufferResize code)

It fixes #156 and tests passes on both Windows and Linux

I think I deserve this PR to be merged If not for nothing else then at least for the design of a buffer pair per plugin.