Adjust waterfall settings to better visualize 2 Hz fading.

[tmiw]

Resolves #79 and #148 by adjusting some of the waterfall settings to prevent filtering out fast fades. This includes:

• Adjusting the built-in IIR filter for the waterfall so that newer data is a bigger contribution to the calculated points.
• Adjusting how new lines are drawn in PlotWaterfall by drawing a MODEM_STATS_NSPEC x 1 temporary image and having wxWidgets resize to the correct width and dy.
• Use a fixed number of pixels/second to avoid issues with fractional positioning and improper WF scrolling speed.

Additionally, this PR adds the ability to average the spectrum plot across 1-3 samples.

[Tyrbiter]

This is a nice improvement, seems to reduce CPU load quite a bit too.

[tmiw]

This is a nice improvement, seems to reduce CPU load quite a bit too.

Neat, I wasn't even aiming for lower CPU 👍

[Tyrbiter]

Would it be possible to have an averaging function on the spectrum display? Maybe allow 1, 2 or 3 sweeps, the new spectrum is a bit noisier and I think it would help to make signals a bit clearer. I am assuming that the waterfall changes can be retained without the spectrum plot affecting those.

[tmiw]

Would it be possible to have an averaging function on the spectrum display? Maybe allow 1, 2 or 3 sweeps, the new spectrum is a bit noisier and I think it would help to make signals a bit clearer. I am assuming that the waterfall changes can be retained without the spectrum plot affecting those.

I added something that I think might do what you're asking. Let me know how it looks? It seems to smooth things out a bit more here, anyway.

[Tyrbiter]

Would it be possible to have an averaging function on the spectrum display? Maybe allow 1, 2 or 3 sweeps, the new spectrum is a bit noisier and I think it would help to make signals a bit clearer. I am assuming that the waterfall changes can be retained without the spectrum plot affecting those.

I added something that I think might do what you're asking. Let me know how it looks? It seems to smooth things out a bit more here, anyway.

This is good for me, the only thing is that the averaging setting is not saved, would be nice if it were.