Adding support for authentication token

[geeosh]

So I'd love to be able to pass a Bearer token as an authentication header in Vandal, as my API is only readable with a user session (via Devise) or Api Token. I'd imagine many APIs would likely have this same constraint. I'd be willing to lend a hand to help, although this repo only contains the compiled JS.

Edit: I found the Vandal gem, so I'd imagine we could add auth headers somewhere around here. It would also involve a bit of UI update to enter them.

[richmolj]

Hey @geeosh!

I would love to get a PR in for this, and think you have the correct read on the issue. That said, I currently use request.ly to authenticate against my API. It's nice because it works not just with Vandal, but even hitting the API in a browser directly (we use JWT headers and not cookies).