update framework

[casperdcl]

Part of #76, closes #11, closes #54, fixes #56

• migrate setup.py => pyproject.toml
  • use SCM versioning
  • drop unused sphinx dependency
• migrate unittest => pytest
  • fix & update some tests
• add CI tests & update workflows
  • purge conda packaging (will do in upstream conda-forge repo instead)
• misc code tidy
  • esp. reduce duplication in test/test__formUI_status_test.py
• add qdarkstyle dependency
• misc minor metadata updates
  • minify licen[cs]e
  • purge changelog in favour of https://github.com/paskino/qt-elements/releases
• enforce annotated tags for releases
• https://github.com/paskino/qt-elements/transfer to @TomographicImaging
  • update URLs

follow-up issues for separate PRs

• [x] #78
• [ ] license text
• [ ] lint