Re #6169. Don't report timing information for skipped or failed tests.
Re #6168. Copy over code to track performance from main repository.

It's not ideal to fork things in this way, but I don't want to have to
check out the mantid repository in order to run this on the system tests.
Merge branch 'feature/6169_performance_monitoring' into develop
Merge branch 'feature/6168_performance_timing' into develop