0.8.0: Wider Linux support, smaller installers, warping_penalty support

0.8.0 modernizes OSC's build/packaging, adds a new warping_penalty parameter the model/mesh warper, removes a few unused/big features/models, and fixes few bugs.

Highlights:

• The mesh warper and model warper now expose a warping_penalty parameter, which penalizes warping the data non-linearly. This can be useful for reducing artifacts and implausible warping - particularly in regions where landmarks are sparse or unevenly distributed. Suggested by Ekaterina Stansfield, from related work (10.1371/journal.pcbi.1014073). The TPS page in docs.opynsim.eu explains it in more detail.
• Linux releases are now built with AlmaLinux 8, which enables building modern C++ code (like OSC's) against older glibc versions (>=2.28). This means OSC's releases are now compatible with Ubuntu >=20.04, Debian >=10, AlmaLinux >=8, RHEL >=8, and OpenSUSE >=15.
• Portable Linux packaging in the form of a .tar.xz archive is now shipped with each release, which should enable using OpenSim Creator on most modern Linux desktop distributions (listed above).

See CHANGELOG.md for a full list of changes.