random fixes that i notices while making documentation

[dmklee]

• put gripper opened and gripper closed in RobotArm class
• fix RobotArm.move_hand_to. need to improve the handling of IK errors or collision errors. and have better control over the rotation, i think the pitch-roll stuff should be in another function
• robotarm init should have headless as optional and assume based on mode. the user can force override this by providing boolean
• add print statement to robot arm init if not calibrated that user should run calibration command; what is the clean way to run calibration scripts
• remove opencv dependencies unless camera is used