Adds and uses a modified_by property in models/work.py This property is used to display the user who last edited the work in the document viewer. Fixes author being set on every edit. Also edited the style-sheet to fix issue i128. Patch by: Lennard de Rijk

# Directions for web crawlers.
# See http://www.robotstxt.org/wc/norobots.html.

User-agent: HTTrack
User-agent: puf
User-agent: MSIECrawler
User-agent: Nutch
Disallow: /