Feature Request: support for multiple databases

[TBeholder]

Instead of single database, support of several independent databases files. So that the user could keep several sets for different purpose ("books", "Caves&Critters", "particle accelerators"…) and switch between them manually or with an option to directly choose an arbitrary starting database file (to be used via custom launchers, and/or if this file is not in the standard path).
Probably it would be best if instances are independent in the database choice.
This would make databases more portable, reduce bookmark clutter and act as simple session support.
May need support for moving document data between databases for backward compatibility (and convenience, when a file view is opened by "open with…" start, rather than added to an existing session).