Add testcases for importing old database files.

Authored by johanneszarl on Feb 27 2019, 10:30 PM.

Description

Add testcases for importing old database files.

Note: while adding these tests, I realized that we no longer support
version 1 files (starting with a "KimDaBa" tag) anyways. I guess that
means we can drop compatibility code for that version...

Details