WIP: New Freesurfer, FSL, Dipy wrappers. Interfaces for Gmsh and GetDP

This is a bit of a mixed of a pull request of stuff required for EEG forward modelling. See http://swederik.github.io/forward

I would say it needs some more cleanup and testing before its ready to merge, though.

There are new wrappers for:

**Freesurfer**
- Transform2Talairach (mris_transform)
- FloodfillSurface (mris_fill)

**FSL**
- BETSurface (betsurf)
- DecomposeTensor (fslmaths -tensor_decomp)

**Dipy**
EstimateConductivity: scales diffusion tensor eigenvalues to estimate conductivity tensor, saves 6 volume file as Nifti

**Gmsh**
[Gmsh](http://geuz.org/gmsh/) is a 3D finite element grid generator with a build-in CAD engine and post-processor. Its design goal is to provide a fast, light and user-friendly meshing tool with parametric input and advanced visualization capabilities.

**GetDP** 
[GetDP](http://geuz.org/getdp/) is a general finite element solver using mixed elements to discretize de Rham-type complexes in one, two and three dimensions. The main feature of GetDP is the closeness between the input data defining discrete problems (written by the user in ASCII data files) and the symbolic mathematical expressions of these problems.