Refactor Database Management

[ronjakrg]

Issue description

With the migration project we have decided to remove the "Manage Database" button from the landing page. Also, we have encountered several problems and weird code snippets regarding the use of databases. We should have deeper look into the codebase and refactor it.

Acceptance Criteria

• The database management is moved to its own settings section
• All tests with mocks are reviewed and considered useful