[PD] object test - matrixctrl, GUI for mtx_mul~

[João Pais]

> Since it outputs 'matrix' messages, it would be nice if it would accept
> 'matrix' messages as input to set the initial state. This would make
> state saving/restoring even simpler.

yes, good idea.

> @colors:
> Mike probably means it'd be nice to be able to set the color of toggled
> and non-toggled cells.

I think too, but just wanted to be sure.