cmtk-reg test doesn't require nat.utils

* in fact, nothing should
Add new xformpoints generic (+ methods for cmtk registrations, matrices etc)

* note that there is still a dependence on write.cmtkreg that needs fixing
Start converting cmtk functions - cmtk.dof2mat/cmtk.mat2dof
CMTK IO: (read|write).cmtk(reg)

+ basic tests