Adds limb move_to_joint_positions optional argument - threshold

* Optional argument allowing the setting of angular success threshold for joint position moves using move_to_joint_positions in limb.py. Default value is the same 0.008726646 (0.5 degrees) from settings.py. This option allows for fine/gross position settings of joint motions programmatically with each motion.

* move_to_joint_positions no longer raises an exception on failure. It will now simply report its timeout, as raising was overkill for this method.