SAK-26179 List PowerPoint as one of the accepted file types by turnitin now.

git-svn-id: https://source.sakaiproject.org/svn/assignment/trunk@309011 66ffb92e-73f9-0310-93c1-f5514f145a0a
SAK-26177 en_GB locale update (grade -> mark).

git-svn-id: https://source.sakaiproject.org/svn/assignment/trunk@309012 66ffb92e-73f9-0310-93c1-f5514f145a0a