Add status config

Hey @ande3577, just wanted to say thanks for maintaining this repo, we've been using your fork and it's been working great.

We have a lot of custom statuses though, some of which we keep as "open" issues but that are basically finished, so they shouldn't show up as available issues in the Stuff To Do page. So, I added a configuration setting which allows you to select specifically which statuses are available.

The default is "all", which simply lists all open issues, to keep the default current behavior the same.

![screen shot 2013-11-18 at 11 01 57 am](https://f.cloud.github.com/assets/93607/1564098/d2744d4e-506a-11e3-8086-c0367df05a2f.png)