Enabling app developers to extend the Properties class

[kirillt]

Currently, an app developer can extend the Properties class, however, they need to create their own version of PropertiesStorage to handle the customized structure. We should consider enhancing PropertiesStorage to support third-party extensions without the need to duplicate the entire code within the app.

A potential solution could be to make PropertiesStorage more flexible and adaptable by generalizing it to operate over a generic P type, rather than having it tightly coupled with the Properties type. This would facilitate easier adaptability and integration with various data structures.

Once we've generalized the PropertiesStorage, we can proceed to shift the existing Properties structure into the ARK Shelf repository.