Add support for patching

[jebbgrenham]

I assume this is programmatically possible. Whether it's a tremendously useful feature I'm not sure.

[fmalcher]

While this would be theoretically possible (the messages look somewhat like SETS^i.6.src^hw.6), I'd rather avoid implementing this if there's not a real need. This first needs a proper design for the API surface, and I feel this could become complex very quickly. The Web UI menu for patching is so horribly complex that I cannot really imagine how this would look in code. We also need to consider the differences between the three Soundcraft Ui models.

So if this feature is important to anyone, please feel free to propose an API design as a discussion base. Thanks!