0.7.0: Additional warping steps, OPynSim/Oscar integration, bugfixes

Externally, 0.7.0 is a minor update that adds additional scaling steps (and options) to the model warping workflow to help with complex warping requirements, improves macOS and Debian/Ubuntu packaging, and includes a few quality-of-life changes and bug fixes.

Internally, 0.7.0 is a large architectural change that makes OpenSim Creator use the upcoming/alpha OPynSim project for its musculoskeletal algorithms and Oscar (internal) for its application engine. The intention is that OpenSim Creator's algorithms (e.g. model warping, shape fitting) will be gradually upstreamed into OPynSim so they can be used via Python. It also means that any new algorithms can first be developed as a Python API, validated, and then shipped to OpenSim Creator. Oscar is only for internal use, but separating it now ensures that it can be used in other (internal) projects and, potentially, further developed into a public C++ library.

See CHANGELOG.md for a full list of changes.