feat(breadcrumb): Display which document is open

- add a breadcrumb which displays the current opened guide or reference

related to CAM-1266
Merge branch 'master' of github.com:camunda/docs.camunda.org

Conflicts:
	site/src/files/app/css/style.css
	site/src/files/app/js/application.js
merge(conflict): Resolve merge conflicts
chore(breadcrumb): Add lost helper method

related to CAM-1266
Merge branch 'master' of github.com:camunda/docs.camunda.org