Overleaf integration through WebEngine

[k3KAW8Pnf7mkmdSMPHz27]

Warning

There is currently no error handling. If you write an incorrect password while logging in to Overleaf it will appear as if you managed to log in but you won't see any projects!

Attempt to continue on #445 using the JavaFX WebEngine.

Todo

• [ ] Is it possible to use WebEngine for this?
  • [ ] Can document changes Overleaf <-> JabRef work
  • [ ] Must be able to store user login information
    • [ ] Make the login retain the information
      • [ ] How to do this securely?
      • [ ] Handle Overleaf refusing the retained information (if old/changed)
  • [ ] Must be able to "clone" a session so that one WebEngine can be used for every local .bib file
    • [ ] For each logged-in user, have a WebEngine instance load the https://www.overleaf.com/project/ page so that the project list can be dynamically updated
      • [ ] Does this detect project changes? (rename)

[k3KAW8Pnf7mkmdSMPHz27]

The next couple of commits will only be readability/refactoring because it is very much needed.