Performance analysis tools

Capture some work done while debugging a specific issue. The code changes here are not required for the issue resolution but might come in handy later.

I have added some more detail to the performance logger output. And also refactored it to make it simpler to port the code to other applications. In particular to the old ZGY-Public library, to be able to compare its performance to OpenZGY.

This pull request also adds a couple of performance oriented unit tests.