* changing references from local planner to controller outside of DWB

* change minimum in DWB planner to be controllers

* Update nav2_core/include/nav2_core/controller.hpp

Co-Authored-By: bpwilcox <bpwilcox@eng.ucsd.edu>

Update index.rst

changing TB3 burger to waffle

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

I was following this guide.
To install ros2-navigation, need to edit `ros2-dashing-navigation2` to `ros-dashing-navigation2`.

When I tried original command from this guide, I got error below.

```bash
$ sudo apt install ros2-dashing-navigation2
Reading package lists... Done
Building dependency tree... 50%
Building dependency tree       
Reading state information... Done
E: Unable to locate package ros2-dashing-navigation2
$ sudo apt install ros2-dashing-nav2-bringup
Reading package lists... Done
Building dependency tree       
Reading state information... Done
E: Unable to locate package ros2-dashing-nav2-bringup
```

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.