Add tests for code accessing the database

[julianbrost]

All code that involves a database has no automatic tests at the moment, which should change. My idea for this would be to pass connection details for a database in an environment variable (if it's missing, those tests could t.Skip(), so that you can still easily run the other tests) and then start writing tests for loading objects/incidents from the database, updating them and so on. In total, this isn't a small task, so I'd do this across multiple PRs, first, establishing the basics with some simple tests, and then adding more tests.