Add params for selecting teleop part for melodic

[708yamaguchi]

I added params to teleop.launch.xml in order to select teleop part.

From ZebraDevs/fetch_ros#101 (review)

[aparker-fetch]

So this is already merged, but I still can't make it work on an 18.04 robot...
for instance:
rosparam get /teleop/use_head shows "false" after editing the launch or doing a rosparam set, but the head can still be moved with the controller.

[708yamaguchi]

Did you build fetch_teleop with this commit (ZebraDevs/fetch_ros@bf353fe )?
This commit enables /teleop/use_head.

Also, I think that rosparam set is not effective to change teleop part because the bool param use_head in joystick_teleop.cpp can be changed only when editting launch file. (Namely, this parameter do not use dynamic_reconfigure.)
https://github.com/fetchrobotics/fetch_ros/blob/melodic-devel/fetch_teleop/src/joystick_teleop.cpp#L731