Drag&drop of patches in CART should swap, not overwrite

[mkruselj]

Currently, when drag&dropping one patch over another in CART, it destructively overwrites the patch you're dropping onto with the patch you're dragging. This also happens in the right side area which lists presets from various sysex files, which means you can easily ruin them completely without undo!

I propose that by default drag&drop swaps the two patches, and if we use Ctrl/Cmd, then it copies. But it should then pop up a dialog asking "Are you sure you want to overwrite patch x with patch y? This operation is destructive and cannot be undone." along with a checkmark "Don't show again".