Add multi-group control panel to Interactive Controls GUI

[swhart115]

This will allow an operator to set the 6-DOF IMs for two or more CARTESIAN groups in RViz, and then use the panel to plan for a composite motion of the robot that achieves all goals (if possible). This functionality needs to be supported by the underlying path planner. For MoveIt! this corresponds to the mistakenly named "subgroup" in the SRDF (it's really a supergroup), i believe. The AtlasPathPlanner also supports this as defined in the MATEC messages that are used for planning.