move collision checker as an input to the configure method of recoveries

adding warning when robot is out of costmap bounds

* Adding the PipelineSequence node

* Rewrite tree to take advantage of the new node.

* Add image generator

* Adding documentation

* Clarifying documentation on PipelineSequence

Reorg bt nav

adding navigation2 new diagram

planner/controller properties to IDs

Minor fix for broken link in build.md file

Fix twice backtracking of path by navfn planner.

Add doxygen doc in nav2_lifecycle_manager header files

changing docker file & removing travis

fix clearing logic for near-max_obj_height instances

Re-enable dwb_plugin tests

- execute gzclient and gzserver individually
- use an argument named headless to execute gzclient

Multiple controller plugins in server for contextual control 

* Attempt to filter out generated message files from code coverage.

* Reduce the number of tests run in Travis to just a single test.

* Filter specific msg packages instead of ros_idl... directories.

* Fixing a typo in the nav_2d_msgs package name.

added ros2-devel as dependency

renamed hpp and cpp files to current bt v3 naming conventions

* added Turtlebot 3 Waffle Gazebo model with depth camera plugin

*changed the robot's shape. used box for the body and cylinder for the wheels 

* removed visuals from urdf. 

*removed meshes from the Gazebo model.

Clean shutdown of system tests