Drag or paste of files to upload in Student / Staff views doesn't work or is dangerous

[alexmcarthur]

In the Student view, pasting a file results in 'Upload undefined' showing on the upload button, and if you hit the button you see 'File uploaded blob' (if you attempt to download the app crashes). Dragging a file to upload works.

In the Staff view, the behaviour is similar but even worse it uploads for all entries in the table, potentially overwriting previous uploads. A dangerous scenario (which has happened more than once in our edX instance) is where you've copied a file and hit paste in the 'Enter Grade' dialog - either by mistake or thinking that the paste buffer has something that you want to paste - the file is then uploaded to all table rows as if you pasted into the Staff dialog beneath.

A suggested fix is to disable paste of files for both the Student and Staff views and only enable drop for the Student view:

            // Set up file upload
            var fileUpload = $(content).find('.fileupload').fileupload({
                url: uploadUrl,
                pasteZone: null,

```...

        // Set up annotated file upload
        $(element).find('#grade-info .fileupload').each(function() {
            var row = $(this).parents("tr");
            var url = staffUploadUrl + "?module_id=" + row.data("module_id");
            var fileUpload = $(this).fileupload({
                url: url,
                pasteZone: null,
                dropZone: null,