Change styling to be more similar to obofoundry.org

[jamesaoverton]

I would like the styling for this editor updated to be a bit closer to the main page of http://obofoundry.org:

1. Title bar: "OBO Metadata Editor"
2. Content centred
3. Table styled somewhat similarly
4. Replace link in first column with a "Edit PURLs" button in a third column

The obofoundry.org site uses Jekyll and Bootstrap 3. The relevant templates are here:

• https://github.com/OBOFoundry/OBOFoundry.github.io/blob/master/_layouts/default.html
• https://github.com/OBOFoundry/OBOFoundry.github.io/tree/master/_includes