Add in-place editing for metadata fields; fixes #211

![screen shot 2014-02-14 at 16 09 13](https://f.cloud.github.com/assets/111218/2176501/727aef78-95d5-11e3-9d92-965f22055913.png)

There's a small problem with the CSS and the height of the text field being a little bigger than the text, but it's pretty close. Maybe @jkeck could take a look at the styling sometime?