Automatic stop/start

[unfa]

I have two ideas for automatic scrolling control:

1. Sync to host or JACK transport (with optional stop delay to add some tail).
2. Use an audio threshold and hold time to pause when no audio is being fed into the spectrograph.

This could help the user analyse what have just happened, without the need to use a separate scrolling control within the spectrogram. It'd also make sure no space is wasted for useless "black" spectrum.

[pdesaulniers]

Interesting ideas :)