Position and velocity frames for RBMs

Adds the ability to have nested multi-coordinate frames, and sets up the state frame of a rigid body manipulator to be composed of the state frames of all of the robots inside that manipulator, with each robot state frame made up of a position frame and velocity frame.
i saw that, but it's not easy to change.  :-/
On Aug 25, 2014, at 6:21 AM, Andres Valenzuela <notifications@github.com> wrote:

> In systems/plants/@RigidBodyManipulator/RigidBodyManipulator.m:
> 
> > @@ -1,8 +1,8 @@
> > -classdef RigidBodyManipulator < Manipulator 
> There are lots of whitespace changes in this file. Could we move those to their own pull request? It makes it hard to review the more substantive changes.
> 
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