Clear output windows previous syntax error or compile messages when saving and there are no more errors

[hermidalc]

Just an annoyance, if I previously had syntax error(s) in my snakemake file and there's message output from those, when I've fixed them and I save the file the previous messages are still there in the output window and I'm no certain that the syntax or compile errors are gone.

[hermidalc]

snakefmt does linting, moved snakemake/snakefmt#155