Tweaks for the dashboard generator

[bendk]

• Spell out units like microseconds and milliseconds. It's easier to know what the scale of the graphs are this way.
• Make histogram graphs logarithmic.
• Split up labeled distribution panels into nightly/beta/release.

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[bendk]

I've harassed Lougenia too much with these dashboard generator PRs. I'm going to spread the work some and give this one to Sammy.

[bendk]

Here's the results on the DISCO dashboard: https://yardstick.mozilla.org/d/disco-main/disco