New IK plugin via ROS service calls, supporting kinematic trees

**Note:** *This commit will not build until the pending PR for moveit_core is merged ros-planning/moveit_core#149*

Create a new plugin in ``moveit_ros_planning`` similar to ``kdl_kinematics_plugin`` that creates an interface between ``moveit_core``'s ``KinematicBase`` and standard ROS Service calls. Also supports the new kinematics trees - solving with more than one tip frame and pose. 

This is used for lisp-based whole body kinematic solvers at the JSK lab, and could also be used for robots like Baxter that have their own IK solver accessible via a ROS Service call.