Refactor SatieConfiguration instantiation

This MR refactors SatieConfiguration instatiation.

From a user's perspective, nothing important has changed. Calling SatieConfiguration.new still works the same from the outside.

This MR allows a SatieConfiguration instance to be created, have it's plugin dictionaries created, but not have any of the instance variables set (listeningFormat, outBusIndex, etc). This basic instantiation is done with the new classmethod *init.

At this point, it is possible to manually add a spatializer into the config's spatializers dictionary. This is useful when doing dev work or simply experimenting. Once you are ready to configure SatieConfiguration fully, you can call the method .configure.

note one possible contentious change is the default value for minOutputBusChannels going from 0 to 2. Essentially, what I'm proposing here is making it so that SatieConfiguration will never set the Server's number of output channels bellow 2. Currently, SatieConfiguration will set the number of ouput channels to whatever its configuration states, even if that means setting it to 0.