Added Moveit adapter package

This implements the Descartes `RobotModel` interface for MoveIt.  The PR includes some parts of PR #13, but not all.  Method implementations for `TrajectoryPt` are not included.  However, these methods will simply be wrappers around RobotModel calls when required.
This way of retrieving the joint values feels uncertain since it is not associated with a particular planning group.  It's very likely that the robot state "variables" and "joints" are identical sets most of the time but It's presumable that there are some cases where this doesn't hold.  I'd recommend using the "copyJointGroupPositions(const std::string& joint_group_name, std::vector<double>& gstate" [here] (http://moveit.ros.org/doxygen/classmoveit_1_1core_1_1RobotState.html#aab69ae00f6d9c0d0249299115afcf7a0) or one of its variants since this returns the joints for the specified planning group.