Underworld

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Fixes:
* SWIG4 compatibility changes.
* libxml2 ubuntu20.04 changes.
* Numpy 1.19 compatability changes.
* Fix `LGPLv3.txt` contents. File incorrect contained
GPLv3 text.

Changes:
* Check for compressibility/penalty clash.
* Update example models for parallel usage.

New:
* Add Dockerfile for Deepnote.
* Add `test_long.sh` long test runner.

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Changes:
* Fix `LGPLv3.txt` contents. File incorrect contained
GPLv3 text.

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Changes:
* Updating Dockerfile to include UWGeodynamics-2.9.4.

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Changes:
* Update citation information in README.md.

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Changes:
* Update Zenodo title.

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Enhancements:
* Update base docker image & implement permission fixes.
* Other docker tweaks and corrections.
* Fixes for image tests