Promting user when attempting to close files

[lepa_01]

Hello! I think it would be a good feature to have CloudCompare promt user before deleting files to prevent accidental deletion of files. This could of course be an optional setting but would help at least a careless user like me. :)

[daniel]

Ah, I think this is already on the TODO list (sadly, it's growing ever and ever, but never shrinks due to the lack of contributors...).