Performance test suite

In Jackrabbit we have a suite of performance tests that track performance characteristics across various JR versions.

We should have a similar test suite where we can track this for Oak across different versions as well as different micro kernel implementations.

Attached is a patch file that basically ports the JR test suite. I have dropped some tests that check functionality that does not exist yet in Oak.
Also the parameter to select a certain repo config has been changed to select a certain micro kernel (see readme).

The child node tests currently test with around 1000 child nodes, as are the limits of reasonable JR child nodes lists. For Oak we might want to have additional tests with way more child nodes.