Enable dragging, copying\cutting and pasting for lines from different folders

[AceKuper]

I never noticed but it turns out you can't actually select things from different folders and cut\copy or edit them, you can only delete them and in some cases wrap them into a new category.

[apocalyptech]

Mm, I can see where that could be useful -- specifically dragging + cut/copy -- but at the moment I'm a bit hesitant to add in support for those. It'd end up complicating the actions a fair bit, including having to check that you don't have both a parent + child selected at once (or figuring out what to do if that is the case), etc. It could just be that this was submitted right after an OpenBLCMM release, so I'm feeling rather lazy, but at the moment I'm disinclined to do this one. I'll leave it open for a bit, though, so we'll see. :)

As for editing across category boundaries, that's definitely not going to happen. There'd be no reasonable way to merge the updated code back in.

Thanks for the report regardless, of course!