Added support for Xbox 360 controller based tele-operation in tutorials.

[dosssman]

Hello @vikashplus

Here is the PR that adds tele-operation based on the Xbox 360 controller added to vtils recently (thanks for the merge).

The tele-operation assumes the camera is facing the robot and the table when tele-operating to collect data for example.
I have followed the poll_keybaord function while adaption to sensor data from the Gamepad class.
One original addition is the use of the controller's X button to slow down the movement of the gripper arm for finer grained tele-operation.

I tested it with:

python robohive/tutorials/ee_teleop.py --input_device gamepad --horizon 5000

Hope this helps.
Best regards.

[vikashplus]

@dosssman -- Thanks for your contributions.