Display mesh feature

This is to answer feature request #394.
Note that VTK handles textures only if loaded from images.
**vtk-5.8 packaged with ubuntu doesn't support multiple textures simultaneous display. The only work around, if your GPU support it, is to rebuild VTK from sources.**

![add_texture_mesh](https://f.cloud.github.com/assets/2897146/1723498/f72b39ac-625a-11e3-9997-72f30f537f6a.png)