feat(ControlBar): Add expand/collapse all buttons

[jeff-phillips-18]

What

Closes #196

Description

Adds the ability for applications to show an expand all and collapse all button on the control bar.
The application must handle the callback and call the new Graph method expandAll or collapseAll. If the application is using a pipeline layout with generate spacer nodes and edges, it must recreate the model and relayout the view.

An example of just how this is done can be found in: PipelineGroupsDemo.collapseAllCallback

Note that there are 2 new methods added to the Graph interface and an optional parameter leafOnly to the getAllChildren method on the Node interface. Any application that is current implementing these interfaces without extending the base implementation will need to adjust accordingly.

Type of change

• Feature

Screen shots / Gifs for design review

[jeff-phillips-18]

Demo app surge: https://expand-collapse-all.surge.sh/

[patternfly-build]

Preview: https://react-topology-pr-topology-203.surge.sh

[jenny-s51]

LGTM. Thank you for adding the documentation @jeff-phillips-18 , will be very helpful when implementing these updates in product.