[baxters_sim_hardware | baxter_sim_kinematics] modified to work baxter_world.launch properly when arg electric_gripper is false

[knorth55]

Require: https://github.com/RethinkRobotics/baxter_common/pull/79

• grav_[right|left]_name and right|left]_tip_name can be changed for other gripper usage because these param was fixed so that we could not modify it easily.
• baxter xacro modified in https://github.com/RethinkRobotics/baxter_common/pull/79 so that gripper is no more loaded to gazebo when you give arg [right|left]_electric_gripper:=false

[knorth55]

@IanTheEngineer can you review this?

[knorth55]

ping

[IanTheEngineer]

resolved by https://github.com/RethinkRobotics/baxter_simulator/pull/118 and https://github.com/RethinkRobotics/baxter_common/pull/90

[knorth55]

Thank you.