Add multi-file drop processing

The Load button's file management dialog has a drop target and an Add a file to the filesystem button.

The button opens an OS file browser dialog that accepts selecting multiple modules and indeed processes them properly (adding them to the file system in one operation); however, while the drop target accepts a multi-file drop event, it does not process any but the first module in the selection.

When multiple modules need to be added to a project, the drop target method isn't as convenient without this multi-file drop capability.