Conditionally show sub-times

[camillobruni]

• Collect and report subTimes like subScores
• Only show times if the global .details CSS class is set (the default view is unaffected)
• Also use .details for displaying displayCategoryScores
• Change uiFriendlyDuration to only report 2 significant digits
• Add Benchmark.prototype.wallTime accessor and report that as well

This is the view you'll get after pressing d or clicking on the score:

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