picking_issue_2

### Integrate baxter as a single arm robot

1.  Modify Baxter properties in `robosuite/models/robots/baxter_robot.py` to fit a single arm robot properties 
2.  Need to find other locations to enable baxter robot deployment in `SingleArmEnv`

[Issue 2](https://github.com/learningLogisticsLab/robosuite/tree/picking_issue_2)