Fix joint names

[studywolf]

Fix in Mujoco interface order of joint_names/ids

• when there were two joints attached to the same body they would be appended to a list that was later reversed. but they needed to be reversed before being appended or else the list of joints would be out of order.
• this caused some very wacky behaviour

[p3jawors]

LGTM, all Mujoco examples working and travis ci tests pass