[Vv] small feature request

[Joel Schaerer]

Hi vv guys,

The vector field overlay dialog box currently restricts the input files
to vf, mhd and mha formats.

Could you add nifti (.nii) and nrrd (.nrrd or .nhdr) support for vector
fields to vv? Even better, add the option to display all files to the
dialog box.

Thanks!

joel