Downsized integration tests for faster test runs

[fhieber]

Our number of integration tests and their size has grown considerably. For faster test runs I downsized most of them by halving model sizes etc.

On Travis this saves ~10 seconds overall time spent in unit/integration tests.

Pull Request Checklist

• Changes are complete (if posting work-in-progress code, prefix your pull request title with '[WIP]'
  until you can check this box.
• Unit tests pass (pytest)
• Passed code style checking (./style-check.sh)
• You have considered writing a test

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[mjdenkowski]

LGTM - I agree with downsizing integration tests as much as possible since we're only looking at whether the components can interact successfully.