Add a shortcut which detects the dragged fileset for certain features + auto-creates a slot

[randomouscrap98]

There are certain oft-used drags which could be made easier. Right now, each file is treated as an individual slot, so you can't for instance drag a .hex and a .bin into the cart builder and expect the .bin to work. However, I could detect if "data" or "save" is in the .bin file, and if the only dragged files are a single .hex file and one or both of those bin files, I could put them all together into a single slot.

But this would require users to name their files appropriately, as there's no good way to tell if a file should be a save file or a data file (at least, not without guessing, which might be bad).