Allow updating of existing mayavi mesh visualizations

[jabooth]

Have this in my jabphd repo - basic use case is you need to render out a whole load of similar meshes with same camera setup:

fig = mlab.figure()
set_camera(fig, nice_pose_camera)
# render_function shows the mesh and returns a function that will update the view
# for new mesh data
update = render_mesh(mean)
mlab.safefig(...)
for mesh in meshes_to_visualize:
    update(mesh)
    mlab.safefig(...)

Issue is it takes something OOP ATM in menpo (per-mesh visualizer) and changes it to persist for many meshes.