Merge points exists in arm_moveit and in the kinesthetic teaching playback

[eshort]

Code for getting and merging plans for keyframe demonstrations is duplicated:

https://github.com/HLP-R/hlpr_manipulation/tree/master/hlpr_manipulation_utils/src/hlpr_manipulation_utils

(in both of the arm moveit files)

and

https://github.com/HLP-R/hlpr_kinesthetic_teaching/blob/master/hlpr_record_demonstration/src/hlpr_record_demonstration/playback_demo_action_server_refactor.py