[merge after #1195, #1237 and #1260] Common safe teleop for JSK mobile robots

[708yamaguchi]

This PR depends on #1195 and #1237

In this pull request, I did

• create common safe teleop system for JSK mobile robots
  • This system allows teleop inputs other than joystick. So, for example, fetch will be able to move with keyboard input.
• apply the system to fetch and PR2
  • This system currently runs on fetch and PR2.
  • For the time being, I'll keep an eye on the behavior.
• update README
  • I update documentation
  • I add system diagram

System diagram (UPDATED in 2020/10/07):

cc @knorth55

[knorth55]

We are testing this PR on Fetch15 and PR1040.

[708yamaguchi]

According to @knorth55 's advice, I update the system.
In the new system,

• I do not use several safe_teleop_base node to reduce CPU load.
• I use different vel_type_selector for fetch and PR2, because fetch does not use /base_controller/cmd_vel topic.
  (If mux_selector.py is used with unknown type topics and wait=True, mux_selector.py does not work. So we need to use different vel_type_selector node)

In addition, I found that wait=True with unknown type topic problem actually occurred In the previous version.
In detail, when fetch is launched, /vel_type_selector is always waiting for the topic and does not work, because /navigation/cmd_vel is a relayed topic and its type is known.

[knorth55]

This PR seems good, and we are testing this on PR1040 and Fetch15.
With this PR, all navigation system is integrated in PR2 and Fetch, thus we can easily move both robot with same topic name space.

[knorth55]

We found that vel_type_selector select default topic name often, so we change default topic to previously selected topic.

[708yamaguchi]

Thank you very much for your help!

@mqcmd196

[708yamaguchi]

I add arg use_safe_teleop.
I need this arg when I want to use mux system in this launch but don't want to use safe teleop node because safe teleop node greatly increases CPU load.

When safe teleop node is not used, /teleop/cmd_vel/unsafe topic is directly relayed to /teleop/cmd_vel topic.

CC @mqcmd196