Add pcad acq sequence fetcher and display app

>
> It requires reading the docs and perhaps buying into the Django forms
> infrastructure, but there are mature ways of doing input validation in
> Django that will pop up red warnings etc. The current code is fine for
> getting something up and running, but we should (collectively) start doing
> things the right way.
>

Sure, yes this was just a copy of your IndexView to get things started.
What kinds of validation do you see as useful for this app (not formatted
like an obsid, doesn't exist as a processed obsid?)?