Nionswift-tool

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- Qt version 5.14 on macOS (local) and Windows.
- Add latency average display (100 rolling samples) when latency display enabled.
- Add backend support for multi-threaded section-serialized rendering.
- Add backend support for section by section drawing for improved performance.
- Add support for layer caching.

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- Add support for Python 3.8. Drop support for Python 3.5.

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- Add support for help event (dynamic tool tips).
- Qt version 5.13 on macOS and Windows.
- Extend sizing policy support.

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- Fix drawing issue for high aspect ratios.

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- Implement high quality image drawing in most cases.
- Do not auto expand when using min width/height. Simplifies layout.
- Improve handling of virtual environments on Linux.
- Qt version 5.12 on Windows.

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- Fix minor scrolling issue in tree widget by expanding area by 2 pixels.
- Fix drawing context save/restore bug.