Send currently opened app & recording ID to data-loaders

[teh-cmc]

So they can decide to either append to the currently opened recording or create a new one when e.g. drag-n-dropping.

Probably want a special shortcut to switch the behavior when drag-n-dropping (e.g. hold shift to split into individual recordings), but that can come in a second iteration I think.

[teh-cmc]

I'm blocked on this for some docs/examples, let's see how hard that is.

[emilk]

Probably want a special shortcut to switch the behavior when drag-n-dropping

Or depending on where in the viewer we drop (this has finally been unblocked in winit)