Re #6169. Don't report timing information for skipped or failed tests.
Re #6169. Add memory reporting to the performance tests.

Added a column to the database and then took the value from there into
the HTML reports (detailed and summary).
Re #6169. Add memory info to main summary page.
Re #6169. Don't bomb out if a date is formatted incorrectly.

For some reason, one of the dates in the first test I did on Windows was
missing the milliseconds, which stopped the script. It really isn't a
big deal if it's missing from the summary page, so just catch the exception
and continue.
Re #6169. Clear the FrameworkManager at the start.

I don't think this should make any difference, but I just want to check.
Re #6169. Try getting the initial memory in init instead of execute.

Some tests load data in their __init__ so I can't clear things out
in execute.
Merge remote-tracking branch 'origin/feature/6169_performance_monitoring'