Image url

Created a field in the database, associated forms and views, spec tests, and validator in lib/validators that allow a user to include an image with their project description by linking to a file hosted on a whitelisted website.

https://www.pivotaltracker.com/story/show/80235250
non-blocking issue, there are inconsistencies in the new lines used, sometimes it is two lines, at other times just one line. It would be better to keep it consistent (one line is our standard)