A default IConnectorFactory using target DataSource for source #21

    * trying to get a DataSource from Cayenne
    * changing package locations for some connector(factory) classes
      to better reflect their position in the framework
    * parameterizing IConnectorFactory. Seems logical that each factory can only create
      one broad category of connectors
    * DataSourceConnectorFactory - a factory based on a map of DataSources
    * a unit test for the non-default behavior of ConnectorService
    * refactoring JdbcConnector into an interface, so that we could have multiple impls.