Gutterball hibernate

This branch removes mongodb from gutterball and instead uses hibernate. Liquibase support has been added to create the DB schema.

Reviewers:  Please take your time with this review. We need to make sure that the model is solid. Keep an eye out for any bits of data that we may want to store but has been left out. I've tried to verify along the way, but feedback was limited.

Nitpicky stuff:
This method performs the key lookup twice when you could do the same operation with only one:

JsonNode node = json.get(key);
return node != null ? node.textValue() : null;