Refs #9486 - Refactoring eea.alchemy utilities and adapters

- Refactoring eea.alchemy utilities and adapters in order to make
  eea.alchemy more extensible from outside this scope.
Refs #9486 - Refactoring alchemy discover utilities and adapters

- Refactoring discover utilities and adapters in order to be able
  to easily extend alchemy functionality outside eea.alchemy package
Refs #9486 - i18n
Refs #9486 - WIP - Add discover utility and adapter for relatedItems

- Add alchemy discover utility and adapter for relatedItems
- Refactoring Alchemy Discoverer UI
Refs #9486 - WIP - Improve Alchemy Discovered UI
Refs #9486 - Implement server-sent events for Alchemy Discoverer

- Add real-time console for Alchemy Discoverer UI in order to see in
  real time what is updated on server.
Merge branch 'master' into auto-relations
Refs #9486 - Disable buttons while working to avoid multiple clicks
Refs #9486 - Support old browsers
Refs #9486 - Cleanup / Refactoring discover adapters.
Refs #9486 - Complete vocabulary for lookin option
Refs #9486 - Schema vocabulary and JS filter long list of checkboxes
Refs #9486 - Implement relatedItems utility and adapter

- Implement utility to extract internal links from text;
- Implement adapter to update relatedItems based on internal links found
  within context metadata;
- Fix all adapters to lookup brain's metadata and then document's metadata;
- Update dependency to beautifulsoup4;
- Update HISTORY.txt
Refs #9486 - Add event subscriber to auto-relate on object modified

- Lookup internal links within content metadata and update related items
  accordingly if auto-relations is enabled in Control Panel;
[JENKINS] - Fix tests