django ajaxuploader upload failure doesn't cause an error message in the browser

[sethwoodworth]

when uploading a non-standard document file format, .ods or an image, everything seems to work with file upload, but ajaxuploader local.py doesn't return a file_pk that is required for metadata submission.

1. make the ajaxuploader support more filetypes that we and google docs support (ods, images)
2. when ajaxuploader doesn't pass a file_pk, have it send an error message to the modal-upload.js script