1. Ensure that kernel-based PVC is performed by default in native space
2. Transform these kernel-based PVC GM_CBF and WM_CBF to standard space by default
3. Calculate median GM CBF value (PVC0) on GM_CBF and WM_CBF PVC maps as well in the population module
4. Make sure point 3 is called with WM_CBF on WM ROIs and GM_CBF on GM ROIs.

Question Henk: when comparing result values, is there an issue that some are median and some are mean?
We use the median in ROIs as often CBF distributions inside ROIs can be non-Gaussian. Likewise, it would be good to have a robust/non-parametric PVC as well (perhaps you want to put this in a separate issue?)

###Release notes
Nothing. Done elsewhere.