Remove clamping from Y-coordinate calculations

[argilo]

The plotter clamps the Y coordinate of many things:

• max line
• average line
• max hold line
• min hold line
• peaks

This is not visible at the bottom of the plot, but at the top of the plot, lines and peaks are drawn across the top of the window:

This seems undesirable and wastes CPU time. I think the clamping can be safely removed. After:

The top-bin highlighting in the histogram plot suffers from a similar problem, but it's not so easy to fix so I'll leave that for later.

[argilo]

@willcode Since you've done a lot of work on the plotter, I expect you might know if there is anything that depends on this clamping. So far I haven't noticed any negative effects.

[willcode]

I don't think it will affect anything else. It was mainly to show that the signal was above scale. But then it should probably do the same thing at the bottom.

[willcode]

The bottom clipping probably has a one-off somewhere.

[argilo]

Yeah, I expect it would need to be plotHeight - 1 to be visible.

Without clamping, it's still possible to tell that the lines have gone out of scale (since they disappear). I suppose with this change you can't tell there's an off-screen peak circle, but I don't think that's a big deal.

I'll let this sit for a bit to see if anyone else has an opinion on clamping vs not.

[willcode]

Some indication of off-scale is nice. We could do it a different way. Nothing great comes to mind at the moment.

[argilo]

I suppose an off-scale indication does become useful when the entire signal is off-screen.

[argilo]

The bottom clipping probably has a one-off somewhere.

I opened #1299 as an alternative, which fixes that bug.