Python support: improve the way we check whether a simulation is valid before running it

New snapshot

libgit2: upgrade to version 1.1.1

Mesa: upgrade to version 21.2.0

Oxygen: upgrade to version 5.85.0

Improve our use of QEventLoop

Simulation support: prevent Python scripts from hanging up the Simulation Experiment view and...

PMR support: ensure that all Git submodules are updated when cloning a PMR workspace

Python support: ensure that data store manipulations are safe

KaTeX: upgrade to version 0.13.13

Documentation: slight improvements

Simulation Experiment view: add a way to plot a parameter against the last used parameter (#2521)

Graph Panel widget: round off axes values whenever possible (#2518)

Qwt: upgrade to version 6.2.0 (#2517)

LLVM+Clang: upgrade to version 12.0.1 (#2515)

New snapshot

CellML Text view: support piecewise statements anywhere (#575)

Simulation Experiment view: random crashes when reloading a file (#2510)

CellML tools: prevent a Qt warning when starting OpenCOR with no file

QScintilla: upgrade to version 2.13.0 (#2503)

QScintilla: upgrade to version 2.13.0 (#2503)

Python support: improve error handling (#2493)

Python support: improve error handling (#2493)

Python support: improve error handling (#2493)

Python support: improve error handling (#2493)

KaTeX: upgrade to version 0.13.11 (#2504)

Oxygen icons: upgraded to version 5.83.0.

Python support: improve error handling (#2493)

Python support: improve error handling (#2493)

Python support: improve error handling (#2493)