Keep uploaded files even if the issue operation has been submitted so they do not have to be uploaded again

Due to browser security it is not possible to prefill the file upload input boxes. So if the attachment field appears on e.g. Create Issue screen, and an error is detected with user input, the user is returned on to the Creat Issue form and is asked to correct their input.

The trouble is that the file attachments are lost, as we are not able to prefll the file inout boxes. Even if we were able to do that, the files would be uploaded the second time, which is a waste of time and bandwidth,

The solution is to keep the files on the server side and attach them once the input is validated.

The UI should let the user know that the files have been uploaded and also should allow the user to upload extra files and cancel attaching existing (already uploaded) files.