Planner node

[rdyro]

Adding the first draft of the path planning node.

The main path planning code is contained in ./ff_path_planning.

This node defines a path planning service, the new service definition is in ./ff_srvs.

See ./ff_path_planning/README.md for more details.

[rdyro]

I added two important improvements:

• hotloading of costs and dynamics files is now possible (in the ff_path_planning package source)
• cost functions now accept and extra argument params_json in the service request in ros as a string
  • this json will be deserialized by the path planning node
  • params will be provided as an extra argument to the cost function
  • this allows costs that change over time, like the end goal or evolving reference trajectory or adding and removing obstacles

[alvinsunyixiao]

Looks good overall! Left a few comments on small details.

[alvinsunyixiao]

This file can be removed since we are using black for style checking

[alvinsunyixiao]

Also can be removed.

[alvinsunyixiao]

Remove to enable testing

Suggested change

	# the following line skips the linter which checks for copyrights
	# comment the line when a copyright and license is added to all source files
	set(ament_cmake_copyright_FOUND TRUE)
	# the following line skips cpplint (only works in a git repo)
	# comment the line when this package is in a git repo and when
	# a copyright and license is added to all source files
	set(ament_cmake_cpplint_FOUND TRUE)

[rdyro]

Reviewed and incorporated changes