Snek and fixes.

This release introduces Snek mode, fixes some minor bugs, addresses some usability gremlins and adjusts some capabilities to make things tidier. Much of this work was done over the summer at the code-sprints at EuroPython 2022 in Dublin. Kudos and thanks to all the new contributors to Mu.

Please provide bug reports or feedback via:

https://github.com/mu-editor/mu/issues/new

• Thanks to @keith-packard for Snek mode. Snek is a Python inspired language for processors too small even to run MicroPython.
• @tmontes contributed changes so Mu builds to Linux AppImages (an easy way to package application for Linux).
• Minor fixes by @stratakis in the Russian translation.
• @carlosperate fixed many minor glitches and gremlins.
• @carlosperate was on fire 🔥 with fixes needed to ensure Mu continues to work with very old versions of OSX (as used in many educational institutions).
• Again, thanks to @carlosperate, AppImage with Wayland no longer the setting of an environment variable to make it work properly.
• The web mode includes simple and easy to use integration with beginner and education friendly web hosts, PythonAnywhere.
• @agdales, @Jeffrey04, @johannaengland and @AnjaVerboven contributed new messages of the day as part of their onboarding at EuroPython.
• @tonybaloney contributed several Windows based fixes and clean-ups.
• @johannaengland and @prcutler were on fire tidying up and fixing docs at EuroPython.
• A bug was fixed in the web mode relating to the resolution and/or recreation of the assets directory (in which images, css and templates were to be found).
• Or friend at Adafruit, @tannewt made the necessary changes so Mu handles OSC commands gracefully (see the PR for more details).
• New contributor, @zigit ensured "Unexpected Maker" based ESP boards are correctly detected.
• Thanks to @Jayman2000, error messages are correctly capitalized (or not) to avoid potential confusion.