Changed Body to body

Due to changes within our mongodb, we're now using lowercase with underscores, rather than PascalCase, so I've modified it such that the tests use body now, rather than Body.

This isn't an ideal change and is a sign of poor design, but I'd rather get something working roughly before getting too bogged down in details. Eventually it would be nice to have some form of Schema so that changes to our external database don't matter to the internal coding. It's also better to use Pythonic naming, rather than PascalCase :)