Python library detection: handle detection errors

[orangecms]

• I'm submitting a ...

  • bug report
  • feature request

• What is the current status?

Regardless of whether the board is not connected, the pslab-python library not found, or Python not found, the app currently just displays that the board is not connected, which leads to misunderstandings.

• What is the expected behavior?

Display a third state for an error with the detection of Python and/or the library. Use some dedicated icon for it. On hover, display a precise message on the detection error, whether Python or the library could not be found.
When the library is not found, it is useful to also print environment variables that concern Python environments plus the Python version and binary path if found. This also helps us debug issues if people run into trouble.

[orangecms]

Some more hints on Python modules and path resolution:
https://realpython.com/lessons/why-cant-python-find-my-modules/

[cynthi8]

duplicate of #685