algorithms.mesh: WarpPoints interface

An interface to Warp vtk meshes from a displacement field. Uses scipy.map_coordinates interpolation.

PS. We should consider adding the following code:
```
from traits.etsconfig.api import ETSConfig
ETSConfig.toolkit = 'null'
```
at the root of nipype imports. As we don't use the gui support of enthought.traits, the toolkit can be set to null and some errors are prevented.

I'm getting satisfactory results using fields generated with FSL and convertwarp. Therefore, I guess any field written by FSL (fields, not coefficients) should work out. But true, we should specify this.

I'll be checking what other interfaces generate compatible fields (and/or implement filters for those that are somehow direct). Basically, any 4D image with 3 components should be enough.

Points that fall outside the FoV of the image, will experiment zero-displacement.