Allowed planning scene monitor to ignore joint states that are not used

[davetcoleman]

Baxter publishes two joint states that are fixed in its URDF. Because these variables do not exists, it throws an exception.

I also noted some potential optimizations that perhaps could be done - I haven't done them yet though because I'm not sure if I understand it fully.

[isucan]

I see the benefits of having just one lookup by joint name, but I would rather use JointModel* instead of an index for passing to the functions. I think that might not need additional functions in RobotModel.

[davetcoleman]

So you agree the current method of doing a map lookup on joint_state->name[i] is wasteful, but you are saying the better fix would be to pass the JointModel pointer instead?

[isucan]

Yes, I agree. I just pushed equivalent changes. Thanks!