Allow joint model group to have use IK solvers with multiple tip frames

**Note:** *This commit will not build until the pending PR for moveit_core is merged ros-planning/moveit_core#149*

Adds functionality to support multiple tip-frames (non-chain kinematics) in IK solutions. 

* For ``JointModelGroup``, changes ``canSetStateFromIK`` to check all available tip frames
* In ``RobotState``, changes ``setFromIK`` to send a pose for all necessary tip frames that an IK solver requires. For instance, if your tree-kinematics IK solver supports 4 tips (4 end effectors, such as two hands and two feet), it will send an IK request to ``KinematicsBase`` with 4 poses.