Draft: pmb.helpers.frontend: Improve shell formatting
Previously, values wouldn't be quoted after being formatted. This means that strings with spaces would be treated as lists, which probably isn't what was intended given that such values would be represented as lists in Python and not strings with spaces. Additionally, lists themselves didn't get formatted properly unless they only were one element long. Improve this by formatting lists as quoted strings with spaces between them.
This could still be improved in various ways, but this still improves matters compared to how it worked before.
Still needs more work. I'm not sure if quoting values always is the right way to go. Feedback is very welcome.