Allow multi-robot setups

[cpr-fer]

This already implements most of the required features for multi robot setups, in addition to cleaning the respecitve files. The biggest issue besides testing is the limitations of xacro:includes with regards to arguments. arguments are always on a global scope, as such the prefix arg can't be used to create multiple robots in a single urdf xacro file. While it is possible to split them up for example how it is done in the two_rebels.launch.py, it is not possible as is to create multiple complete kinematics as planned to be done in the rebel_on_platform files.

For this the different kinematics need to be put into their own macros, in a similar fashion as e.g. UR does it with their ur_macro.urdf.xacro. This creates some extra LoC and work, but should be the best compromise for having a choosable number of robots.

[cpr-fer]

Changes up until now:

• Changed structure of urdf/xacro files to a macro system
• Added joint/link prefixes
• Delayed startup of control nodes seems to no longer work with multiple event listeners, thus I removed it and it still seems to work fine.
• Renaming of links:
  • Final link of robot arms from hand to flange
  • Mobile platform chassis to base_link

TODO:

• [x] Autoformat/lint xml files
• [x] Fix remaining missmatches caused by the chassis to base_link rename
• [x] Remove mock_hardware as the default launch parameter
• [x] Add a diagram for the urdf/xacro structure
• [x] Change the grippers to the new macro format
• [x] Test the changes

Maybe/Seperate PRs:

• Macro for chosing between protocols/mock hardware?
• Get MoveIt and Nav2 to run with multiple robots
• Transform the rebel base_links in the two rebel example to different positions

[cpr-fer]

This should be mergable, but only after some further testing on monday

[cpr-fer]

Testing revealed some further issues and todos:

• [x] hardware_protocol launch argument needs a description
• [x] Add documentation about it to the readme
• [x] rebel_on_platform and nav2 startup for din rail modules fails regularly (fixed by 5b523e5)
• [x] Nav2 rviz start fails
• [x] Test again

For a seperate issue:

• MoveIt with mock_hardware rebel does not allow executing trajectories

[cpr-fer]

More things found:

• [x] The rebel_on_platform combination seems to cause issues with the CAN communication, as the socket buffer fills up quickly
• [ ] YAML wildcards/parameter overwrites could simplyfy the setup
• [x] GroupAction scoping seems to cause issues with the "controller_manager_name" launch parameter for some reason
• [x] It appears as the wait_for_controller_manager event works with scoping again just fine, so it should probably be added again
• [ ] The loading of robot descriptions is not yet thought out completly. Currently each base launch file loads their own robot descriptions and does the xacro substitutions. According to (TODO: Add link) this is not the prefered ROS way. Instead the top level launch file should create a robot description publisher for the entire scene. This means the xacro substitutions must be done there as well instead of the lower level launch files, and the lower level launch files must listen to robot description (should be done by default) and not parse some xacro file themselves
• [ ] Once this is done adapt two_rebels and rebel_on_platform launch files

[cpr-fer]

If the CI passes I will merge the PR today and move the remaining TODOs into follow up issues/PRs. The main goal has been achieved and writing more beautiful launch files is not the highest priority right now.

Edit: two_rebels launchfile is broken, so still no merge...

[cpr-fer]

Well, some issues will persist after merging, but I'm splitting this into multiple new issues/PRs since the foundational work is done and the PR has already grown too much