a binder that can launch different versions of jupyterlab dev builds

[tonyfast]

Begin adding doit tasks to build a binder. to begin we're gunna steal lots of others have done.

addresses #18

https://gke.mybinder.org/v2/gh/deathbeds/accessibility/binder

[tonyfast]

I am pretty sure this binder is working now for testing; at least i'm getting the red bar.

I am not sure the best way to verify it is working.

@bollwyvl could you review some of the targets i commented that went to the build folder. i couldn't set those up correct enough to get doit to work.

[bollwyvl]

@goanpeca raised the point of how the heck do we use this... we can add a README/CONTRIBUTING update, but didn't want to step on any toes as we're moving forward...

[isabela-pf]

I have a draft PR for updating the readme and can add something there if you know what you want. I think @tonyfast could probably also make commits to that PR too since he's in the accessibility organization.

[tonyfast]

y'all think we could merge this?

[blink1073]

Fantastic, I'm excited to see this in action!

[isabela-pf]

🎉 Ahhhh! I'm so excited. Congrats on merging this and thanks for your work!