Vertex groups/weights for Splines

Splines should support vertex groups and weights, so that the influence of deformation modifiers can be better controlled.

Right now I am working on a rig for waving tentacles. Splines are working best so far, at least in terms of easy control and good deformation. However, there is no way to limit the effect of the wave modifier along the spline, so the tentacles are sometimes pulled off the place they need to stay attached to.

Vertex groups would be a convenient way to fix this.