Add visualizer for which digital states are high/low

[bparks13]

In the canvas for DigitalIO, display some sort of indicator that changes states during acquisition, mirroring the digital buttons/port states. e.g., when the moon button is pressed, light up a representation of the moon button in the canvas.

This should help people to understand / decode the TTL event word, since it can be confusing to understand what it is, especially if multiple states change simultaneously.