TEST: Stick URDF

Launch the UNROTATED (working) example with:

```bash
roslaunch franka_gazebo panda.launch \
  use_gripper:=false \
  headless:=false \
  paused:=true \
  initial_joint_positions:="-J panda_joint6 $(calc 'deg2rad(-90)')"
```

and step the simulation a few times.

For the bugged example switch the commented region in `panda_gazebo.xacro` for
joint6 and launch the ROTATED (bugged) example with:

```bash
roslaunch franka_gazebo panda.launch \
  use_gripper:=false \
  headless:=false \
  paused:=true \
  initial_joint_positions:="-J panda_joint6 $(calc 'deg2rad(90)')"
```