[Test] Add UI tests

[bugwelle]

Personal backlog item

We currently have no proper UI tests nor proper tests that check a running MediaElch instance. That needs to change.

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Ideas:

• [x] scraper & integration tests should not require command line arguments; should be default --> 4a85c7efbbd07148cd892158da012e5804a0e20e
• [ ] Docker environment for clean setup; may need some display app (xf...?)
• [ ] One full test, that does a common MediaElch setup, which may take 20min to execute; the happy path should work
• [ ] More fine grained integration tests for things like combobox tests, etc.