addressed feedback, added template for addLayer, added stubbed footprint, passing all linters & uncrustify

replaced old costmap with costmap_2d in WorldModel

Port costmap2d buffer + tf_sensor_msgs local port 

Dockerfile update to fix build fails
Also build fixes for ROS2 master branches

Addressing lint error

Since we likely won't implement non-ROS robots, remove the abstract base class
and make the Robot class be a ROS robot. The Robot class will contain the functionality
common to all ROS robots. There can be derived classes that add functionality that is
not common to all ROS robots.

Also, since I'm modifying the SimpleNavigator, update the ROS log messages so that
they don't (redundantly) include the module name since it's already in the output.

Fixing small bug within AMCL: checking for the last laser message received when no message has been received at all.

* First revision of mission executor readme
* Update nav2_mission_executor/README.md
* Address review feedback

Cleanup of some time math and conversions between type.

Fixing several linter failures

Fixing linter failures in nav2_util

* human readable and more meaningful info/debug logs
* change paths to include full representations
* cleanup
* resolve crdelsey's grammar concern
* oops missed a tag
* shutdown infos

Created readme files for Dijkstra Planner, System Tests and Planner Component Tests.

Removed  _CORRECTED suffix from ODOM_MODEL

Build CI using ros2 master nightly build

This resolves #71

* Documentation on local planner changes for ROS 2.

* Adding more detail on local planner operatiion in the new model.

* Addressing feedback.

* Fixing issue links