Tweak styles and characteristics of the charts

[julienw]

I've been testing with this URL (compare with the beta branch) that has a few retriggers.

I tweaked a few things with this patch (each line is a separate commit):

• By using triangles instead of circles, we get a sharper shape, and therefore it's easier to distinguish them when they're closer
• all graphs are now on the same scale, which makes them easier to compare
• the perceived width of the runs density graph is now smaller
• the runs density graph is now (IMO) nicer to interact with
• the bandwidth for the KDE computation is more sensible, at least for the graphs I tried them with. Hopefully it's OK for others too.

Before:

After:

[netlify[bot]]

✅ Deploy Preview for mozilla-perfcompare ready!

Name	Link
🔨 Latest commit	35e4a308cc8a73f07ccc4b46ee1ea6dbf45095fa
🔍 Latest deploy log	https://app.netlify.com/sites/mozilla-perfcompare/deploys/66b5eec04e5dff0008d0e6d3
😎 Deploy Preview	https://deploy-preview-709--mozilla-perfcompare.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site configuration.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 85.56%. Comparing base (f0c4cb3) to head (35e4a30).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## beta #709 +/- ## ========================================== + Coverage 85.48% 85.56% +0.08% ========================================== Files 83 83 Lines 2143 2155 +12 Branches 393 393 ========================================== + Hits 1832 1844 +12 Misses 274 274 Partials 37 37 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.