Book, Database, and Spreadsheet should be subtypes of Information Medium Artifact

[APCox]

Some subtypes of 'Information Bearing Artifact' (IBA) may be better represented as 'Information Medium Artifact' (IMA). For example, Book, Database, and Spreadsheet. As they are currently defined, there are cannot exist a "blank" or "empty" instance of these types. Switching them to be IMAs would enable greater nuance.

This is a task to create a PR with the proposed changes.