Add support for creating scripts for branches. A start for issue #10

Here's a start at least. What do you think about the direction?

Another option might be to return a special code if the branch doesn't have a script, just like it does if it hasn't gotten to the last build, yet. As it stands, it should return 404 if there's no repo+branch combo defined.

There's quite a bit of duplication of the code to build a query for a deploy. I'd like to clean that up before the merge, but I wanted to get this up for comment, first.