Currently Unity does not officially support Silverlight and therefore it does not provide support to configure the container from a file.
To customize your container’s configuration, you will need to override the
ConfigureContainer method in your Bootstrapper class with the custom configuration for your application’s container via code.
Perhaps you could find useful the following article (from Composite Application Guidance for WPF documentation) to understand the container configuration better:
Regarding your other questions, it could be considered that the “equivalent” of the
App.config.xml file from Composite WPF is the ModulesCatalog.xaml.
In that file you can specify the modules to be loaded and how they will be loaded (on demand or when the application starts for example).
Another way to configure the modules that will be loaded is via code.
This two cases are covered by the Modularity Quickstarts released in the latest
Prism-v2 drop (drop 6):
Static Module Loading QuickStart (Code)
Remote Module Loading QuickStart (ModuleCatalog)
This is not necessarily the final design of Modularity in Prism-v2, as the team will likely make some modifications to it for future drops .
Please let me know if this helps.