Added mongolab support.

Note that when MongoServiceCreator creates the MongoDB connection, it uses the "uri" field from the credentials as-is if the field is present:

`mongoDbFactory = new SimpleMongoDbFactory(new MongoURI(serviceInfo.getUri()));`

This is by request from our MongoDB partner, since they would like to be able to control aspets of the connection using query parameters in the URI if/when necessary. This is reasonable since MongoDB supports connection strings in the form of URIs natively (with the MongoURI class).