Re-add support for global planner behavior

[andrewjong]

Within Behavior Tree, some button like "Global Planning Mode".
This puts the robot in a state where it's open to receiving Service Calls for whatever global planners it has available.

Each service call is custom to the specific global planner. In the future these will be transmitted from the ground control station.

When the service call comes in, it triggers the appropriate global planner. The global planner then publishes its plan to the /ROBOT_NAME/global_reference_trajectory topic.

The local planner subscribes to that and sends local plans as trajectory segments to the /robot_1/trajectory_controller/trajectory_segment_to_add topic.

[andrewjong]

Done in #118