Use OpenCTM encoding of data

[bcipolli]

From @binarybottle in email:

@r03ert0 recommended months ago that we convert surface meshes (via meshlab command line) to openctm format, which is FAST!

[cMadan]

OpenCTM is really great. For some code to start with, he uses it here (https://github.com/r03ert0/qcsurf). I adapted that code, though my version is a bit more commented for the conversion part (https://github.com/cMadan/brain3d).