Improve handling of attachments to deleted transactions

[mtotschnig]

Currently, we have the "Stale images" entry in the Settings that appears when attachments are left over from deleted transactions.
User suggests to allow to deal with attachments immediately when transactions are deleted:
I suggest that the current dialog appear and if there are any image attachments in the batch, add 3 radio buttons: (a) keep the (stale) images in internal, the current default, (b) delete the images, or (c) move all the images to the external folder. I believe (b) and (c) are the current functions allowed in the "Stale images" section, but this would allow the user to bypass going to Settings for the desired result. Using this method would apply to all the transactions in the batch. For separate treatments, you would have to select and delete the transactions in sub-batches or individually.