Another update to the PC app + design docs

[system_arch.uxf]
* Added. Block diagram for the example project.

[comHandler.cs]
* Updated for the changes to the communication protocol.

[Form1.cs]
* Uncoupling some tasks from the GUI handling thread to the new
MusicController class.

[MusicController.cs]
* New file
* Adds interfaces to the fileparsers, MusicPlayer, and ComHandler. This
is so that the GUI remains that: an interface

[MusicPlayer.cs]
* Removed GetStatus(), stub function from the previous implementation of
this class.
* Removed the ability to store tracks, this as should be handled by
MusicController

[MusicSynchroizer.cs]
* More or less renamed to MusicController.cs, but otherwise got rid of
this class.

[SongData.cs]
* New file
* Figure one class per file.