restructuring - largely revamped the internal organization of the function, changed the grid handling, fixed a bug in the interpolation that caused it to be plotted 0.5 voxel shifted. See http://bugzilla.fcdonders.nl/show_bug.cgi?id=2640


git-svn-id: svn+ssh://svn.fcdonders.nl/home/svnroot/fieldtrip/trunk@9710 0cf7c7f0-3615-4144-b4e6-68da3bce3cd0