more intelligent handling of output folder

[VladimirAlexiev]

If there's something in the output folder, it causes this error:

PermissionError: [WinError 5] Access is denied: 'ontology'

Then it deletes the folder (not just folder contents), which is:

• not user friendly since if I had something useful there...
• not useful, since it cannot run when the output folder does not exist

I'd suggest it should create the folder if missing, and have an option to overwrite an existing folder