Reduce hardcoded delay after 3D import

There is 2 second hardcoded delay after 3D import puppet exists after the import. According to code comment this is done to allow little time for file operations to finish. IIRC if there is no extra delay, import will sometimes fail on creator side as not all files can be seen yet.

It should be possible to reduce this delay while still keeping operations reliable. Maybe QFileSystemWatcher can be utilized to check when it's safe to exit puppet process?