[JWS] Add support for generic DB type

Images currently only support MySQL, PostgreSQL and MongoDB out of the box. Adding support for configuring a "generic" datasource would enable users to more easily integrate other DB types into their applications. Configuration for a generic DB would most likely entail an expanded property set, as the users would need to configure the driver class, etc. (although we could make this part of the property set, with defaults for the existing supported DB types).