Enable handling of vector images with more than 3 components in SlicerCore

[bpaniagua]

This will allow seeing every component in the Volumes module and avoid the DWI hack (adding DWMRI_b-value:=1000.000000
modality:=DWMRI at the end of a nhdr file)

[phcerdan]

Not an exact fix, but functionality to extract single components from vector images was merged into slicer core here: Slicer/Slicer#967