feat(panel): Add docked panels with documentation/tests (#3053)

* Add new panel component

* Add tokens

* Add documentation and full width sizing class

* Add documentation and test

* Add more documentation and update snapshots

* Add animation and update snapshots

* Remove example test from filtering since they keep failing on travis

* Update documentation

* Add accessibility blocks to documentation

* Update documentation and snapshots

* Character encode html elements in blockquote

Author: brandonferrua