throttled onwheel event

[kwcantrell]

I don't know if this an issue was created for this but I just tried using empress on a mac laptop and the zoom functionality was incredibly sensitive, which caused the tree to zoom in/out incredibly fast. This PR fixes that issue by throttling the .onwheel event to fire at most 1 every 50 milliseconds.

[kwcantrell]

McHelper is failing to connect (see #517) which is causing the build to fail.

[fedarko]

Nice catch, thank you!

Not to split hairs, but would a slightly lower throttle value be ok? On an Ubuntu laptop, 50 ms seems too jerky for me (compared to the previous settings) -- 10 ms feels better. (I captured two GIFs comparing the settings, but I'm not sure these will be useful due to frame-rate stuff...)

50 ms	10 ms

I guess we should ideally try to pick the lowest value that allows Mac users to control things well. That all being said, I suspect that there probably isn't a "perfect" value here, especially since lots of things like touchpad sensitivity are up to the user -- I'm fine choosing a setting that works reasonably well for both of us, and in the future we could make this configurable in the side panel or something if desired.

McHelper is failing to connect (see #517) which is causing the build to fail.

Weird -- not sure why this is happening. In any case, this PR looks fine, so I'm happy to merge it in when we agree on a value.

[kwcantrell]

agreed @fedarko, ideally there should be some 'sensitivity' adjuster. I lowered the throttle to 10. I tried lower numbers (as I felt my normal laptop worked perfect before the throttle) but it seemed a bit fast for mac. So, 10 seems to be the optimal number to make everyone happy.

[fedarko]

Thanks @kwcantrell!