System constraints

Replaces stateConstraint method logic with a list of constraint objects for each DrakeSystem.  These can handled more elegantly (preserving the structure of the constraints, and avoiding function handles) by the optimization classes.  

Taking another crack at finishing and merging this (just had a rough time bringing it back in line w/ master).  

just didn't make it yet.  would be great to add this.

On Oct 5, 2014, at 9:43 PM, Andres Valenzuela <notifications@github.com> wrote:

> In systems/plants/RigidBodyLoop.m:
> 
> > +      axis=[1;0;0];  % default according to URDF documentation
> > +      axisnode = node.getElementsByTagName('axis').item(0);
> > +      if ~isempty(axisnode)
> > +        if axisnode.hasAttribute('xyz')
> > +          axis = reshape(parseParamString(model,robotnum,char(axisnode.getAttribute('xyz'))),3,1);
> > +          axis = axis/(norm(axis)+eps); % normalize
> > +        end
> > +      end
> > +      loop.axis = axis;
> > +
> > +      type = char(node.getAttribute('type'));
> > +      if ~strcmpi(type,'continuous')
> > +        error(['joint type ',type,' not supported (yet?)']);
> > +      end
> > +
> > +      % todo: add relativeQuatConstraint, too
> Was there a problem with drakeFunction.kinematic.RelativeQuaternion? Or did this just not make it into this round?
> 
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