GitLab

This reverts commit a4f5f8f0.

- moved draw_sample() and inverse_draw_sample() to EndomorphicOperator
- inverse_draw_sample() is always possible if draw_samples() is implemented (see EndomorphicOperator)
- changed WienerCurvature draw_sample() to probably better version
- implemented both functions in DiagonalOperator and ScalingOperator properly (i.e. check for positive definiteness)