Awood/gb liquibase

You will need to run `bundle install` before the `liquibase:changeset` task will work.
I thought it was safe, but I was completely wrong.  According to the [docs](http://www.liquibase.org/documentation/changeset.html): "Each changeSet tag is uniquely identified by the combination of the 'id' tag, the 'author' tag, and the changelog file classpath name."

I will drop this commit and change the buildr code to use the legacy time format.  I think I'm going to let the format be a per project setting though so Gutterball can still use a more human friendly format.  Thoughts on this?