Submission system - first round of content edits

Edited messages.xml file to incorporate some content edits from https://docs.google.com/a/datadryad.org/document/d/1cyBCUBRihCKtVAqFNNMKgQS81qbrInoyJOIuM7gG-W0/edit. Verified on localhost. Still working on content updates that require editing files other than messages.xml.