Support DSI-Studio SRC files

[neurolabusc]

DSI-Studio stores voxel-based data in it proprietary Matlab-based SRC format. The upcoming commit supports loading these images. Once the PR is merged, this features will be a new live demo. This format inherent limitations in this format (e.g. spatial transformation matrix not encoded, so origin and oblique rotations are not known). The reader is rudimentary, and does not yet support preserving the btable that would allow display of V1 lines.