Option for cancel button to delete file

[dj-riley]

I believe it would be useful to add a toggle setting that will enable additional functionality on the 'Cancel' button: such that when the Cancel button is clicked, the pasted image is deleted and removed from your vault. Currently, the Cancel button dismisses the modal but the image remains in your vault with a "Pasted Image XXXX" filename. Often times I find myself changing my mind about the image being pasted once the preview is displayed - typically when dealing with images with transparent backgrounds. If the image isn't transparent as expected, the process involves clicking the Cancel button and then manually locating and deleting the pasted image. If this new option were enabled, clicking the Cancel button would then dismiss the modal AND delete the pasted image.

[phanex]

I'll accede to the request