Enable multiple laser scanners (multirobot & rigid)

[SteveMacenski]

and name counter in laser assistant

[SteveMacenski]

multi-laser branch seems to work fine until the first optimiation update, perhaps an assumption that breaks down in enumeration or chain linking, shouldn't be too hard to add 👍

Task list:

• Get optimizer / pose-graph in line with multi laser
• reprocessing transform with multiple scanners -- best practice?
• update deserialization look for N lasers to reload (if needed)
• get the transforms across working less jerky
• test across Magazino's open source dataset in Cartographer docs
• rejoice!
• localization mode buffer needs to be mapped to laser name and clearing on a per-sensor basis.
• for multirobot, odometry getters should be mapped to sensor names as well.

Another option is an embedded object to create a composite laser scan from all scans on a robot. The issue then is synchronizing them, which would be a pain

[SteveMacenski]

https://github.com/SteveMacenski/slam_toolbox/compare/multi_laser

Closer...