[ModalManager] uses instance (arrow) functions which makes hard to extend

[ianschmitz]

I was trying to extend the ModalManager class to add some additional functionality when add/remove are called. This was a little difficult since the functions inside of ModalManager use instance (arrow) functions. Ideally I would love to do something like:

class CustomModalManager extends ModalManager {
  add() {
    super.add();
    // some additional stuff
  }
  ...
}

But ended up having to do some monkey patching to get it to play nicely. Would you accept a PR to change to normal prototype methods instead of instance methods?

[oliviertassinari]

@ianschmitz Do you want to remove the arrow functions?

[ianschmitz]

I'm on it