Instead of passing an 'onload' JS function as part of the AJAX response for each step of the workflow,
we specify all onload handlers up-front when initialising ModalWorkflow, and return a 'step' field
in the response to indicate which one to trigger.
* Expose Draftail package as global variable for reuse
* Expose Wagtail React components for reuse
* Expose Draftail-related React components for reuse
Updated snapshots due to the upgrade and failing ExplorerPanel test. This was due to the shallow call being made earlier than defining the document.body
Update to React 16
Update other dependencies
Stylelint updates
Remove unused imports
Update babel and gulp packages
Update package-lock
