Add more intuitive arguments to default.launch

[egordon]

(1) Add all controllers from personalrobotics/pr_ros_controllers#26 to YAML file for use.

(2) Modify default.launch to be sensitive to arm version and DOF. In preparation for making the repo more robot-agnostic.

Note: this should not change any functionality as-is. It is mostly a refactor in preparation for future PRs.

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Before creating a pull request

• [ N/A ] Document new methods and classes
• [ N/A ] Format code with make format

Before merging a pull request

• [ N/A ] Add unit test(s) for this change

[amalnanavati]

LGTM. I'm approving because the comments are either minor or just clarifying comments. If you end up addressing the minor comment I'll re-approve, but I also think it's fine to merge it in as-is.