`ResultsSummary` improvements

[loganharbour]

Motivation

Looking to add a few quality of life improvements to the results summary comments.

Design

• Increase the default "floor" for whether or not to show test times as changed to 2 seconds. This means that tests won't be checked for run-time differences unless the head test takes more than 2 seconds.
• Ensure that formatting in tables is consistent; currently some times are reported as "0.8" for example, but they should be reported as "0.80" (exactly 2 values after the decimal; :.2f formatting with python)
• When a comparison is available, show the commit hash of the comparison and the URL to CIVET job that produced those tests

Impact

New capabilities.