DataSupplier – interface, through which the datasources refer to Middleware for loading and
saving entities. The standard implementation simply delegates to DataManager.
A screen can define its implementation of the DataSupplier in dataSupplier attribute
of the window element. Such own implementation may, for example, call an additional middleware
block for loading data for the screen from different database.
A reference to DataSupplier can be obtained either by injection into a screen controller or
through the DsContext or Datasource instances. In both cases, an own implementation
is returned if defined for the screen.
