Solution working tree restructure.

Moved Cartage source into its own sub folder under 'src' folder.
Replaced used of class 'ICartInfoStoreProviderFactory' with 'Pug.Application.Data.IApplicationData<Dp>' generic class to allow specialized 'ICartInfoStoreProvider' interface.

- Introduced new data store provider type parameter in 'Cart' class
- Introduced new data store provider type parameter in 'Cartage' class
Enable setting cart item line attribute individually.
Refactoring of entity classes to use type interfaces.