WIP: Test Fisher matrix using definition

It was long requested to have a way to test Fisher matrices for their correctness. In this branch, we test whether the sample expectation value

\left<\frac{\partial H(d|x)}{\partial x}\frac{\partial H(d|x)}{\partial x^\dagger}\right>_{P(d|x)}

agrees with the actual fisher metric. We do so by comparing the fisher application at one random vector with the expectation value defined above. The test is however only statistically true for the limit of many data realizations d, and thus the error margins have to be taken large in order to avoid false postives.