Unify joint control / link state calls

[ChengshuLi]

We are using

• pybullet calls: e.g. p.resetJointState
• igibson.external.pybullet_tools.utils calls: e.g. set_joint_positions
• RobotJoint function calls in robot_base.py: e.g. reset_state

It might be better to unify all of these.

[cgokmen]

There's usually no good reason to use the p. versions directly, too - with the pybullet_tools version you can see the arguments & it will put the results in easy-to-use namedtuples.